arxiv:1612.02688v1 [astro-ph.ga] 8 dec 2016

Preprint typeset using LATEX style emulateapj v 121611

SEARCH FOR INTERSTELLAR MONOHYDRIC THIOLS

Prasanta Gorai1 Ankan Das1 Amaresh Das21 Bhalamurugan Sivaraman3 Emmanuel E Etim45 Sandip KChakrabarti61

1Indian Centre for Space Physics 43 Chalantika Garia Station Rd Kolkata 700084 India2 Ramakrishna Mission Residential College Narendrapur Kolkata 700103 West Bengal India

3 Atomic Molecular and Optical Physics Division Physical Research Laboratory Ahmedabad 380009 India4 Indian Institute of Science Bangalore India-560012

5 Department of Chemical Sciences Federal University Wukari Nigeria and6 SN Bose National Centre for Basic Sciences Salt Lake Kolkata 700106 India

ABSTRACT

It has been pointed out by various astronomers that very interesting relationship exists betweeninterstellar alcohols and the corresponding thiols (sulfur analogue of alcohols) as far as the spectro-scopic properties and chemical abundances are concerned Monohydric alcohols such as methanoland ethanol are widely observed and 1-propanol is recently claimed to have been seen in Orion KLAmong the monohydric thiols methanethiol (chemical analogue of methanol) has been firmly de-tected in Orion KL and Sgr B2(N2) and ethanethiol (chemical analogue of ethanol) has been claimedto be observed in Sgr B2(N2) though the confirmation of this detection is yet to come It is very likelythat higher order thiols could be observed in these regions In this paper we study the formationof monohydric alcohols and their thiol analogues Based on our quantum chemical calculation andchemical modeling we find that lsquoTgrsquo conformer of 1-propanethiol is a good candidate of astronomicalinterest We present various spectroscopically relevant parameters of this molecule to assist its futuredetection in the Interstellar medium (ISM)

Subject headings Astrochemistry spectra ISM molecules ISM abundances ISM evolution meth-ods numerical

1 INTRODUCTION

Starting from the detection of first carbon containing molecule methylidyne radical (CH) in 1937 (Swings amp Rosen-field 1937) almost 200 molecules including neutrals radicals and ions have been observed in the interstellar medium orcircumstellar shells and almost 60 molecules have been observed in comets A mismatch between the cosmic abundanceof sulfur and observed abundances of S-bearing species is well known (Palumbo et al 1997) Particularly around thedense cloud regions this inequality is severe (Tieftrunk et al 1994 Palumbo et al 1997) Around the diffuse cloud andhighly ionized regions sulfur related species roughly resemble the cosmic abundance sim 10minus5 (Savage amp Sembach 1996Howk et al 2006) Earlier Millar amp Herbst (1990) Jansen et al (1995) suggested that S SO CS and H2S may explainthe missing sulfur problem though our knowledge about the CS related species is very limited Recently Muller et al(2015) suggested that at 400 K more than 50 of the sulfur budget is shared by CS and H2CS and remainder residesin the form of SO and SO2 for hot source Sgr B2(N) Several experiments were carried out to propose the abundantS-bearing species on interstellar grains Outcome of these experiments proposed that OCS (Garozzo et al 2010) CS2

(Ferrante et al 2008) hydrated sulfuric acid (Scappini et al 2003) would act as a sink for the interstellar sulfur Tilldate only two sulfur related molecules (OCS and SO2) had been detected on grain surface with full confidence thusthe exact reservoir of sulfur is yet to be known with certainty (Wood et al 2015 Palumbo et al 1995 Boogert et al1997)

Among the monohydric alcohols methanol (CH3OH) is the simplest alcohol which is widely observed both in gasand solid phases (Tielend amp Allamandola 1987) of the ISM Major portion of the interstellar grain mantle is found tobe covered with methanol (Gibb et al 2004 Das et al 2008a Das Acharyya amp Chakrabarti 2010 Das amp Chakrabarti2011 Das et al 2016) Gas phase abundance of methanol relative to H2 is found to be in the range of 10minus9 incold dark clouds to 10minus6 in hot molecular cores (Charnley et al 1995) The presence of Ethanol (C2H5OH) (secondalcohol in this homologous series) is observed in star-forming regions in the range of 10minus8 minus 10minus6 (Millar et al 1988Turner 1991) Propanol is the next alcohol in the series of monohydric alcohols which may belong in two differentforms normal(n)-propanol (CH3CH2CH2OH) and 2-propanol (CH3CHOHCH3) Recently n-propanol (1-propanol)was claimed to be detected towards Orion KL by Tercero et al (2015) with a column density of 6 (10 plusmn 02 times 1015)cmminus2 whereas the presence of 2-propanol is yet to be verified

It is now confirmed that methanol and ethanol are mainly produced on dust grains during the cold phase andevaporate from warm dust grains in latter stages of evolution Following this trend even higher order alcohols wouldbe produced on interstellar grains In case of thiols sulfur takes the place of oxygen in the hydroxyl group of analcohol Similar to their alcohol analogues these thiols are mainly produced on the grain surface and are evaporatedin suitable time Tentative detection of Methanethiol (CH3SH) in Sgr B2 had been done by Turner (1977) Later this

1ankandasgmailcom

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2 Gorai et al

claim had been confirmed by Linke et al (1979) and showed that CH3SHCH3OH ratio is close to the cosmic SOratio Recently Majumdar et al (2016) detected CH3SH in IRAS 16293-2422 and Kolesnikova et al (2014) reportedthe detection of C2H5SH in hot core Orion KL But very recent observation by Muller et al (2015) suggested that thedetection of C2H5SH in Orion KL is uncertain Presence of higher order thiols are yet to be seen

In this paper we discuss the formation of monohydric alcohols and their thiol analogues First we identify the moststable conformer of alcohols and their thiols Then we develop a chemical network to study the formation of all thesespecies From the outcome of our chemical modeling most probable new candidate for the astronomical detectionis found out Moreover a detailed spectroscopic study is carried out to set a guideline for observing this species innear future This paper is organized as follows Section 2 describes the quantum chemical calculation to find outthe most stable conformers Section 3 contains chemical modeling Section 4 contains the information regarding thespectroscopic parameters for the detection of the next probable candidate Finally in Section 5 we make concludingremarks

2 SEARCH FOR MOST STABLE CONFORMATIONAL ISOMERS

All the quantum chemical calculations reported here are calculated by using Gaussian 09 program (Frisch et al 2009Foresman amp Frisch 1996) Each optimized structure is verified by avoiding the imaginary frequency With the advanceof quantum chemical calculation a proper choice of Method and basis sets are required to compute the molecularproperties

According to IUPAC definition of a conformer conformational isomerism is a form of stereo isomerism in whichthe isomers can be inter-converted exclusively by rotations about formally single bonds It is expected that the moststable conformer would be the most probable candidate for the astronomical detection In this attempt here beforeconstructing our chemical model we search for the various conformers of the monohydric alcohols and their thiolsthrough relaxed potential energy surface (PES) scan of dihedral angles PES scan results are displayed in Fig 1and relative energies of the conformers are pointed out in Table 1 2-propanol2-propanethiol is the structural isomerof 1-propanol1-propanethiol for the sake of completeness we discuss about their conformers as well For all thesecalculation we use Moslashller-Plesset perturbation theory (MP2) with the Peterson and Dunningrsquos correlation consistentbasis set (cc-pVTZ) (Peterson amp Dunning 2002) of Gaussian 09 software Results of the PES scans are the following

21 Methanol amp methanethiol

Methanol and methanethiol both show internal rotation of CH3 group From relaxed potential energy surface scan(minus180 to +180 of dihedral angle ang(H3C1O6H5)) we have shown that methanol and methanethiol both exist inthe most stable state at plusmn 180 of the dihedral angle on PES On the other hand there exist three different maximafor both methanol and methanethiol at plusmn 120 and at 0 Relative energies are pointed out in Table 1

22 Ethanol amp ethanethiol

In case of ethanol and ethanethiol both have two types of internal rotation around OHSH group and CH3 groupDue to internal rotation of the OHSH group of ethanolethanethiol it may exist in four different forms For ethanoltransanti conformation (dihedral angle ang(C1C5O8H9) =180) is the minimum energy state on PES The gaucheconformer (dihedral angle ang(C1C5O8H9) = plusmn60) is situated slightly upper on the PES The relative energy betweenthe trans and gauche conformer is 0877 cmminus1 When the dihedral angle is plusmn 120 conformers are called eclipsedThe relative energy between trans and eclipsed conformer is 415 cmminus1 When the dihedral angle is 0 it is called cisconformer which is also situated at higher energy state on the PES The relative energy between trans and cis conformeris 456 cmminus1 (13 Kcalmol) Whereas for ethanethiol the most stable conformer is gauche in which ang(C1C5S8H9)dihedral angle is at plusmn 60 Relative energy between gauche and trans conformer is 170 cmminus1 (049 Kcalmol) relativeenergy between gauche and eclipsed conformer is 524 cmminus1 (150 Kcalmol) and the relative energy between gaucheand cis conformer is 541 cmminus1 (155 Kcalmol) Due to CH3 rotation there would also be some changes in the energybetween the conformers but all are higher as compared to the most stable one

23 1-propanol and 1-propanethiol

Maeda et al (2006) discussed five possible conformational isomers of 1-propanol originating from alternate structureof the central (C1C5O8H9) and (O8C5C1H3) skeletal chains These five forms are Transminus trans (Tt) T ransminusgauche (Tg) Gauche minus trans (Gt) Gauche minus gauche (Gg) and Gauche minus gauche

prime(Gg

prime) Based on the relative

energies of these conformers Abdurakhmanov amp Ismailzade (1987) find out that Tg conformer has the lowest energyHowever Lotta et al (1984) Kisiel et al (2010) predicted that Gt conformer has the lowest energy Our quantumchemical study also finds that Gt conformer has the lowest energy As in earlier studies in terms of their relativeenergies we found that 1-propanol conformer follows the sequence of Gt Gg

prime Gg Tg T t in the ascending order of

relative energiesSimilar studies have been carried out for 1-propanethiol Since 1-propanethiol is yet to be detected in the ISM

perspective views of its five possible staggered conformers originating from the combination of trans and gaucheconfiguration is shown in Fig 2 Our calculation reveals that Tg configuration has the lowest energies Relativeenergies of all the conformers with respect to the Tg conformer are shown in Table 1

Alcohols amp Thiols 3

0

05

1

15

-200 -100 0 100 200

Dihedral angle

-05

0

05

1

15

Ene

rgy

(in K

calm

ol)

Methanol

Methanethiol

-1

0

1

-200 -100 0 100 200

Dihedral angle

-2

0

2

4

-100 0 100 200

Dihedral angle

Ethanol

Ene

rgy

(in K

calm

ol) Ethanethiol

Ethanol

Ethanethiol

C1-C5-O8-H9

C1-C5-S8-H9

O8-C5-C1-H3

S8-C5-C1-H3

-3

-2

-1

0

1

2

-200 -100 0 100 200

Dihedral angle

0

1

-100 0 100 200

Dihedral angle

1-propanol

Ene

rgy

(in K

calm

ol)

1-propanethiol

1-propanol

1-propanethiol

C1-C5-O8-H9

C1-C5-S8-H9

O8-C5-C1-H3

S8-C5-C1-H3

-05

0

05

1

15

2

-200 -100 0 100 200

Dihedral angle

-05

0

05

1

15

2

Ene

rgy

(in K

calm

ol)

2-Propanol

2-Propanethiol

Fig 1mdash Relaxed potential energy surface scan of dihedral angle of monohydric alcohols and their thiol analogues using MP2cc-pVTZ level oftheory

4 Gorai et al

TABLE 1Relative energies of various conformers of alcohols and their thiol analogues

Species Conformer ∆E in cmminus1 (Kcalmol)

HCOH plusmn 180 0 (0)

HCOH plusmn 60 04389 (00013)

Methanol HCOH 120 395 (113)

HCOH 0 395 (113)

HCSH plusmn 180 0 (0)

HCSH plusmn 60 0877 (00025)

Methanethiol HCSH plusmn 120 445 (127)

HCSH 0 445 (127)

trans 0 (0)

gauche 23 (0066)

Ethanol eclipsed 415 (119)

cis 456 (130)

gauche CCSH 0 (0)

trans CCSH 1700 (049)

Ethanethiol eclipsed 5240 (150)

cis 541 (155)

Gt 0 (0)

Gg 67 (019)

1-propanol Ggprime

35 (001)

Tt 95 (027)

Tg 80 (023)

Tg 0 (0)

Tt 216 (062)

1-propanethiol Gt 318 (091)

Ggprime

63 (018)

Gg 46 (013)

gauche 0 (0)

2-propanol trans 836 (024)

trans 0 (0)

2-propanethiol gauche 12 (0034)

Fig 2mdash Five possible conformers of 1-propanethiol


Depending on the rotation of the dihedral angle ang(H10C9O11H12)ang(H10C9S11H12) 2-propanol2-propanethiolmay exist in two forms gauche and trans gauche conformer is found to be stable for 2-propanol whereas in case of2-propanethiol trans conformer is found to be stable Since 2-propanol2-propanethiol is a secondary alcoholthiolwe are not considering this in our chemical modeling

3 CHEMICAL MODELING


TABLE 2Ice phase production of alcohols and their corresponding thiols

Reaction Energy Barrier (K) Reference

Methanol

H + CO rarr HCO 1000 H

H + CO rarr HOC 1000 H

H + HCO rarr H2CO 0 H

H + HOC rarr CHOH 0 H

CH + OH rarr CHOH 0 H

H + H2CO rarr HCO + H2 1850 H

H + CHOH rarr CH2OH 0 H

OH + CH2 rarr CH2OH 0 H

O + CH3 rarr CH2OH 0 H

H + CH2OH rarr CH3OH 0 H

Methanethiol

H + CS rarr HCS 1000 H

H + HCS rarr H2CS 0 H

H + H2CS rarr CH3S 1000 M

S + CH3 rarr CH3S 0

H + H2CS rarr HCS + H2 1000 M

H + H2CS rarr CH2SH 1000 M

CH2 + HS rarr CH2SH 0

H + CH3S rarr CH3SH 0 M

H + CH2SH rarr CH3SH

Ethanol

C2H5 + OH rarr C2H5OH 0 H

CH2OH + CH3 rarr C2H5OH 0

C2H5 + O rarr C2H5O 0

H + C2H5O rarr C2H5OH 0

Ethanethiol

C2H5 + HS rarr C2H5SH 0 M

CH2SH + CH3 rarr C2H5SH 0 M

S + C2H5 rarr C2H5S 0 M

H + C2H5S rarr C2H5SH 0 M

CH3 + CH3S rarr C2H5SH 0

1-propanol(CH3CH2CH2OH)

C2H + H2O rarr HCCCHO + H 0

O + C3H3 rarr HCCCHO + H 0

H + HCCCHO rarr HCCHCHO 1688

H + HCCHCHO rarr H2CCHCHO 0

H + H2CCHCHO rarr CH2CH2CHO 2891

H + CH2CH2CHO rarr CH3CH2CHO 0

H + CH3CH2CHO rarr CH3CH2CH2O 2274

H + CH3CH2CH2O rarr CH3CH2CH2OH 0

C2H5 + CH2OH rarr CH3CH2CH2OH 0

1-propanethiol(CH3CH2CH2SH)

C2H + H2S rarr HCCCHS + H 0

S + C3H3 rarr HCCCHS + H 0

H + HCCCHS rarr HCCHCHS 2167

H + HCCHCHS rarr H2CCHCHS 0

H + H2CCHCHS rarr CH2CH2CHS 2659

H + CH2CH2CHS rarr CH3CH2CHS

H + CH3CH2CHS rarr CH3CH2CH2S 734

H + CH3CH2CH2S rarr CH3CH2CH2SH 0

C2H5 + CH2SH rarr CH3CH2CH2SH 0

H reaction taken from Hasegawa Herbst amp Leung (1992) M reaction taken from Muller et al (2015)

31 Chemical network

For the purpose of chemical modeling we use our large gas-grain chemical network (Das et al 2008b 2013ab)Gas-grain interactions are considered to mimic the most realistic scenario of the ISM We assume that gas and grainsare coupled through accretion and various desorption mechanisms such as thermal non-thermal (Garrod amp Herbst2006) and cosmic-ray desorption processes Our present gas phase chemical network consist of 6628 reactions between684 gas phase species and surface chemical network consists of 487 reactions between 316 surface species We adoptour gas phase chemical network from the UMIST 2006 database (Woodall et al 2007) Our gas phase network containssome deuterated reactions as well (Das et al 2015ab Sahu et al 2015) For the grain surface reaction network weprimarily follow Hasegawa Herbst amp Leung (1992) and for the ice phase deuterium fractionation reactions we followCaselli et al (2002) Cazaux et al (2010) Das et al (2016) Though we have the deuterated species in our networkwe are not considering the deuterium chemistry here for the sake of simplicity

Here we are mainly concentrating on the formation of monohydric alcohols and their thiol analogues Thesemolecules are mainly formed on the dust surface Chemical enrichment of the interstellar grain mantle depends onthe binding energies (Ed) and barriers against diffusion (Eb) of the adsorbed species The binding energies of thesespecies are available from past studies (Allen amp Robinson 1977 Tielens amp Allamandola 1987 Hasegawa Herbst ampLeung 1992 Hasegawa amp Herbst 1993) But these binding energies mostly pertain to silicates Binding energy of themost important surface species (with ice) which are mostly controlling the chemical composition of the interstellargrain mantle are available from some recent studies (Cuppen amp Herbst 2007 Garrod 2013) We use these energies inour model For the rest of the species for which binding energies were unavailable from these papers we keep it thesame as the past studies We use binding energies against diffusion equal to 05Ed (Garrod 2013) for our calculations

6 Gorai et al

TABLE 3Peak abundance of ice phase alcohols and their thiols with respect to H nuclei in all forms

Isothermal phase Warm-up phase

Species gas phase ice phase gas phase (temp in K) ice phase (temp in K)

Methanol 175 times 10minus9 212 times 10minus5 698 times 10minus6(1060) 186 times 10minus5(1024)

Ethanol 838 times 10minus11 466 times 10minus11 126 times 10minus6(1202) 200 times 10minus6(714)

1-propanol 645 times 10minus20 184 times 10minus17 429 times 10minus7(1206) 476 times 10minus7(1061)

Methanethiol 106 times 10minus10 162 times 10minus8 216 times 10minus8(1073) 458 times 10minus8(312)

Ethanethiol 304 times 10minus22 523 times 10minus20 545 times 10minus9(1200) 102 times 10minus8(662)

1-propanethiol 294 times 10minus27 600 times 10minus25 371 times 10minus10(1227) 373 times 10minus10(1084)

TABLE 4Molecular ratio of some species

after 10 times 106 years after 15 times 106 years after 20 times 106 years Observed

CH3OHC2H5OH

2663 1879 324 45t78m1

CH3OHCH3CH2CH2OH

208 times 109 3485 779 2700t

C2H5OHCH3CH2CH2OH

773843 185 240 60t

CH3SHC2H5SH

261 times 1011 708 455 ge 21m31m1

CH3OHCH3SH

269 3443 1127 120m 5700m1

C2H5OHC2H5SH

262 times 108 129 157 125m225m1

mMuller et al (2015) from observation m1Muller et al (2015) from modeling tTercero et al (2015) from observation

Our ice phase network contains other reactions mentioned in Hasegawa Herbst amp Leung (1992) In Table 2 we haveshown only some grain phase reactions which may lead to the formation of these alcohols and their thiol analoguesDruard amp Wakelam (2012) shows that chemistry of sulfur may be very different from the chemistry of other chemicalelements They considered sulfur polymers (Sn) and polysulphanes (H2Sn) as the potential candidates of the sulfurrefractory residue Here we have considered all the sulfur related reactions used in Druard amp Wakelam (2012) For theformation of Methanol we use the pathways proposed by Hasegawa Herbst amp Leung (1992) Methanethiol productionis followed by Muller et al (2015) For the ethanol production we assume barrier-less addition between C2H5 and OHradical (Hasegawa Herbst amp Leung 1992) CH2OH and CH3 radical and hydrogenation reaction with C2H5O Forthe production of Ethanethiol we use the pathways proposed by Muller et al (2015) Reaction references are alsonoted in Table 2 Since for the formation of 1-propanol and 1-propanethiol no pathways were available we use somenew pathways for the formation of these species in ice phase For the formation of the 1-propanol we have consideredtwo radical-molecular ice phase reactions followed by 4 successive hydrogen addition reactions Similar sequence isalso considered for the formation of 1-propanethiol In addition we also have considered the radical radical reactionbetween C2H5 and CH2OH for the formation of 1-propanol and radical-radical reaction between C2H5 and CH2SHfor the formation of 1-propanethiol As like the other radical-molecular reactions considered in Hasegawa Herbst ampLeung (1992) here also we are assuming the barrier-less nature of these reactions Rate coefficients of this type ofreactions thus depend upon the adopted adsorption energies and would process in each encounter Among the foursuccessive hydrogen addition reactions considered here hydrogen addition reaction in second and fourth steps of 1-propanol and 1-propanethiol would be considered as radical-radical interaction and thus barrierless in nature But thefirst and third steps of this sequence is the neutral-neutral reaction which must contain some activation barrier Wehave carried out quantum chemical calculation to find out suitable transition states for these neutral-neutral reactionsQST2 calculation with B3LYP6-31+G(d) method is employed for this computation and obtained activation barriersfor these neutral-neutral reactions are pointed out in the second column of Table 2 Though 2-propanol and 2-propanethiol are the structural isomers of 1-propanol and 1-propanethiol respectively we are not considering theirformation in the present study For the destruction of ice phase species we consider the photo-dissociation reactionsby direct interstellar photons and cosmic ray induced photons

We do not use any new gas phase formation of these species In our model gas and grains are continu-ously interacting with each other and exchanging their chemical components Surface species could populate thegas phase by various evaporation mechanism considered here namely thermal desorption cosmic ray induceddesorption and reactive non-thermal desorption (here we assume a non-thermal desorption factor to be 001)For the destruction of gas phase alcohols and their corresponding thiols we use destruction by most abundantions (H3

+ CH4+ C+ HCO+ N+ O+H3O+ CH+ O2+ H+ He+ CH3

+) dissociative recombination photo-dissociation and dissociation by cosmic rays

32 Physical condition

In order to realistically model the physical parameters we consider a warm-up model (Quan et al 2016) Initialphase of this model is the isothermal phase (T = 10 K) followed by a warm-up phase Both phases have the same


constant density (nH = 104 cmminus3) and a visual extinction of 10 Second phase starts with 10 K and ends at 200K Here it is assumed that the isothermal phase lasts for 106 years and the warm-up phase for another 106 yearsInitial abundances are taken from Druard amp Wakelam (2012) except the sulfur abundance Druard amp Wakelam (2012)considered abundance of S+ in its cosmic value sim 15times 10minus5 (Sofia et al 1994) Here we are assuming much reducedS+ abundance (80 times 10minus8) as used in Leung Herbst amp Huebner (1984) Hydrogens are mostly assumed to be in theform of molecular hydrogen These molecular hydrogens were mainly formed on the dust surfaces (Biham et al 2001Chakrabarti et al 2006ab) in earlier stages For the ionization of the medium we assume a cosmic ray ionization rateof 13 times 10minus17 sminus1

33 Modeling results

In Fig 3 we have shown the time evolution of gas phase (solid curve) and ice phase (dotted curve) alcohols and theirthiol analogues Upper panel shows the isothermal phase and lower panel shows the warm-up phase In the isothermalphase it is clear that ice phase methanol ethanol and methanethiol are efficiently produced Some portions of theseabundant ice phase species is readily transfered to the gas phase via various desorption mechanisms At the beginningof the warm-up phase ice phase production of ethanol ethanethiol 1-propanol and 1-propanethiol increases due tothe increase in the mobility of the surface species involved in the reactions In Table 3 we have pointed out the peakabundances of these alcohols and their thiol analogues for both the phases In the warm-up phase peak abundancesof these species along with the temperatures related to these peak values are also pointed out

It is fascinating to indicate from Table 3 that among all the species shown in Table 3 methanol is the only onewhich is most efficiently produced in the isothermal (T = 10 K) phase compare to the warm-up phase Its peakice phase abundance in isothermal phase is found to be 212 times 10minus5 with respect to total H nuclei whereas in thewarm-up phase its peak abundance of 186 times 10minus5 is appearing around 1024 K In compare to the isothermal phaseabundances of the other ice phase species are seemed to be significantly higher in the warm-up phase For examplepeak abundance of ice phase methanethiol appears around 31 K production ethanol and ethanethiol is found to beefficient around 66 minus 71 K and efficient production of 1-propanol and 1-propanethiol is found to be around 106 minus 108K Formation of ethanol ethanethiol 1-propanol and 1-propanethiol at such high temperatures occurs mainly due tothe radical radical reactions It is essential to point out that adopted adsorption energies of some of these key radicals(CH3 C2H5 OH SH CH2OH CH2SH are 1175 K 2110 K 2850 K 1500 K 5080 K 5084 K) available from someearlier studies (Garrod 2013 Cuppen amp Herbst 2007 Hasegawa amp Herbst 1993)

Since we are mainly considering the ice phase production of these species appearance of the peak gas phaseabundance is highly related to their respective adsorption energies For example in case of methanol and methanethiolwe have assumed the adsorption energy 5530 K and 5534 K respectively and from Table 3 the resulting peak gasphase abundances of methanol and methanethiol seems around 106 minus 107 K For the ethanol ethanethiol propanoland 1-propanethiol much higher adsorption energies are assumed (6260 K 6230 K 6260 K and 6260 K for ethanolethanethiol 1-propanol and 1-propanethiol respectively) which ensures the peak gas phase abundance of these speciesaround 120 minus 123 K

In Table 4 we have shown molecular ratio (gas phase) of these alcohols and their thiol analogue Since chemicalevolution is highly time dependent phenomenon ratios are shown for various time scales 10 times 106 years correspondsto the end of the isothermal phase 15times 106 years corresponds to the middle age of the warm-up phase and 20times 106

years is related to the end of the warm-up phase Gas phase ratio of the observed and other modeling results arealso shown Gas phase observational ratios are taken from Tercero et al (2015) and Muller et al (2015) whereas hotcore modeling results is taken from Muller et al (2015) It is interesting to note that around the isothermal phasegas phase abundance of methanol methanethiol and ethanol is in the range of 10minus9 minus 10minus11 whereas the gas phaseabundances of other species is negligible which yields a much higher molecular ratios of some species Beyond 10times106

years mobility of the surface species rapidly increases and yields significant production of negligible species At theend of warm-up phase we are having a reasonable values of these ratios

4 SPECTROSCOPY

41 Vibrational Spectroscopy

Our results suggest that 1-propanethiol would be a probable candidate for the astronomical detection Here wecalculate the IR spectrum of 1-propanethiol for the sake of completeness Moreover vibrational spectral informationof its one structural isomer 2-propanethiol is also presented In Table 5 we assigned different modes of vibrations alongwith frequency and intensity of these species Ice phase absorbance is shown in terms of integral absorption coefficientin cm moleculeminus1 We compare our results with the existing experimental results Gaussian 09 program is used for allthese calculations Water is used as a solvent to compute vibrational spectroscopy using Polarizable Continuum Model(PCM) with the integral equation formalism variant (IEFPCM) as a default Self-consistent Reaction Field (SCRF)method IEFPCM model is considered to be a convenient one because the second derivative of energy with respectto coordinate (bond distance bond angle) is available for this model and also its analytic form is available For thiscomputations we use DFT method with B3LYP functional and higher order basis set 6-311g++(2df2pd) (Choi etal 2008) for better accuracy A comparison between our calculated IR spectrum band with the existing experimentalresults of 1- proapnethiol and 2-propanethiol (Torgrimsen amp Klaeboe 1970 Smith et al 1968) are shown in Table5 It is clear from the table that our results are in excellent agreement with the existing experimental values Mostintense band of 1-propanethiol appears at 323 microm (309147 cmminus1) and 324 microm (308519 cmminus1) due to CH3 and CH2

8 Gorai et al

TABLE 5vibrational frequencies of 1-propanethiol and 2-propanethiol in water ice phase at B3LYP6-311g++(2df2pd) method and

basis set

Species Peak position Integral absorbance Band experimental values

in cmminus1 coefficient assignment wavenumber

(in microm) in cm moleculeminus1 (in cmminus1)

11238 (8898) 230times10minus19 skeletal deformation

19124 (5229) 307times10minus18 SH torsion

23145 (4320) 892times10minus20 CH3 torsion


35801 (2793) 551times10minus20 CCC bending

69354 (1441) 169times10minus18 CS stretching 700a

73309 (1364) 119times10minus18 CH2 rocking 728a

80520 (1241) 853times10minus19 SH out of plane bending 814a

89645 (1115) 106times10minus18 CH3 bendingCC stretching

92264 (1083) 301times10minus19 CH2 twisting

103161 (969) 772times10minus20 CC stretching

109801 (910) 691times10minus19 CH2 rocking

112858 (886) 217times10minus18 CC stretching 1105a

1-propanethiol (Tg) 125295 (798) 961times10minus19 CH2 twisting 1243a

128052 (780) 349times10minus18 CH2 wagging 1300a



140751 (710) 415times10minus19 CH3 out of plane bending 1384a

146593 (682) 536times10minus19 CH2 scissoring 1456a

148297 (674) 176times10minus19 CH2 scissoring

148936 (671) 171times10minus18 CH3 deformation


266677 (374) 479times10minus19 SH stretching 2598a

302545 (330) 163times10minus18 CH3CH2 symmetric stretching 2838a

302823 (330) 434times10minus18 CH2 symmetric stretching 2848a

305601 (327) 1053times10minus18 CH2 antisymmetric stretching 2945a



309147 (323) 841times10minus18 CH3 antisymmetric stretching


22530 (4438) 370times10minus18 SH torsion 185b

23002 (4347) 850times10minus20 CH3 torsion 230b


32381 (3088) 481times10minus19 CCS bending 325b


40772 (2452) 505times10minus20 CCC bending 410b

59492 (1680) 209times10minus18 CS stretching 620b

85573 (1168) 184times10minus18 SH out of plane bending


93874 (1065) 370times10minus20 CH3 bending



2-propanethiol (Trans) 112678 (887) 361times10minus19 CC stretching


129752 (770) 484times10minus18 CH out of plane bending

133678 (748) 184times10minus19 CH bending

140078 (713) 139times10minus18 CH3 out of plane bending






266662 (375) 506times10minus19 SH stretching

302165 (330) 478times10minus18 CH3 symmetric stretchin

302743 (330) 842times10minus18 CH3 symmetric stretching

305092 (327) 752times10minus19 CH stretching




310997 (321) 721times10minus18 CH3 antisymmetric stretchingaTorgrimsen amp Klaeboe (1970) and references therein bSmith et al (1968) from experiment


TABLE 6Rotational quartic and sextic centrifugal distortion constants of 1-propanethiol and 2-propanethiol

Species Rotationalconstantswith equi-librium (e)amp groundvibrationalstate (0)geometry

Values in MHz withDFT(HF) method

Experimentallyobtainedground-statevalues in MHz

Distortionalconstants

Values in KHz with DFT(HF)method

Ae 24213642(2442975) ∆J 0296911(0208512)

Be 2312864( 233788) ∆K 21457798(6184248)

Ce 2222041( 224540) ∆JK 29811(422776)

δ1 -00455(-0039844)

A0 2323981( 2363275) 234290 δ2 04518(996033)

B0 230132( 232806) 234529 ΦJ -090726times10minus08(-02571times10minus07)

1-propanethiol (Tg) C0 219916( 222675) 225018 ΦK 0419723times10minus02(045931times10minus01)

ΦJK 0153284times10minus04(048892times10minus05)

ΦKJ 0863327times10minus03( 040468times10minus02)

φJ -0454229times10minus07(-020575times10minus07)

φK 0194759times10minus02(011375times10minus02)

φJK 0557817times10minus05(031203times10minus08)

Ae 7886965( 793821) ∆J 1246( 1043)

Be 4341565( 439957) ∆K 6799(5473)

Ce 3118889( 315254) DJK 2184(3312)

δ1 3728(0265)

A0 778214(784142) 789265 δ2 03805(1933)

B0 430651(436693) 441442 ΦJ 0108001times10minus07( 015733times10minus06)

2-propanethiol (trans) C0 308777(312421) 315803 ΦK 0144633times10minus04(054329times10minus05)

ΦJK 0562981times10minus05( 013656times10minus05)

ΦKJ 0115468times10minus04(019811times10minus05)

φJ 0818191times10minus07(071495times10minus07)


φJK 0439650times10minus05(012349times10minus05)k Kisiel et al (2010) l Griffith amp Boggs (1975)

TABLE 7Dipole moments of alcohols and their thiol analogues by using HF6-31g(d) Experimental values are given within the

bracket

Dipole moment components in Debye

Species microa microb microc microT otal

Methanol -15406 (144a) 10537 (0899a) 00 18665 (169a)

Methanethiol 14683(1312b) 10152(0758b) -00001 17851(151b)

Ethanol -00541(0046c) 17374(1438c) 00000 178383HF 153DFT (1441c)

Ethanethiol 00431(106d) 18597(117d) 000 18602 (150d)

1-propanol (Gt) 080180574x (032e104914e2) 10022 1086x(123e109705e2) 10743 0922x(094e109042e2) 16737 153x(158e114145e2)

1-propanethiol (Tg) 17638 -00840 08186 19463(16f )

2-propanol (gauche) -12070(1114g) -07023(0737g) 09868(08129g) 19163(156g)

2-propanethiol (trans) 04034 18685 000 19115 (161f )aIvash amp Dennison (1953) bTsunekawa et al (1989) cTakano et al (1968) dSchmidt amp Quade (1975) eAbdurakhmanov et al (1970) fLide

(2001) gHirota (1979) xcalculation at MP2cc-pVTZ level

stretching band respectively with the integral absorbance coefficient of 881times10minus18 and 841times10minus18 cm moleculeminus1

respectively Most intense band of 2-propanethiol belongs to 325 microm (307879 cmminus1) which corresponds to the integralabsorbance coefficient of 150 times 10minus17 cm moleculeminus1

Figure 4 shows isotopic variation of vibrational spectra of 1-propanethiol We show isotopic variation by changing themass of carbon (C = 12 and 13 isotopic mass) and sulfur atoms (S = 32 and 34 isotopic mass) The result shows thatbending mode and stretching modes are shifted towards lower wavenumbers CS stretching for CH3CH2

12CH232SH

mode with wavenumber 7004 cmminus1 is shifted to 69801 cmminus1 CH2 wagging mode having wavenumber 127169 cmminus1 isshifted to 126514 cmminus1 and CH2 antisymmetric stretching with wavenumber 311192 cmminus1 is shifted to the wavenum-ber 310118 cmminus1 due to change of isotopic mass of a carbon atom of CH2 group (CH3CH2

13CH232SH)

42 Rotational Spectroscopy

Till date most of the species are observed in the interstellar medium or circumstellar shells by their rotationaltransitions Chakrabarti et al (2015) Majumdar Das amp Chakrabarti (2014ab) Majumdar et al (2013a 2012) pointedout the need for theoretical calculations for firm identification of some unknown species in the ISM Species whichhave permanent dipole moments show their rotational transitions Here we compute various rotational parameters

10 Gorai et al

1e+03 1e+04 1e+05 1e+06

log (time) year

1e-25

1e-20

1e-15

1e-10

1e-05

log

(a

bu

nd

an

ce)

Methanol (gas)

Ethanol (gas)

Propanol (gas)

Methanethiol (gas)

Ethanethiol (gas)

Propanethiol (gas)

Methanol (ice)

Ethanol (ice)

Propanol (ice)

Methanethiol (ice)

Ethanethiol (ice)

Propanethiol (ice)

10e+06 12e+06 14e+06 16e+06 18e+06 20e+06

Time (year)

1e-14

1e-12

1e-10

1e-08

1e-06

1e-04

log

(a

bu

nd

an

ce)

480 860 1240 1620 2000

Temperature (K)

Isothermal phase

Warm-up phase

Fig 3mdash Time evolution of monohydric alcohols and their thiol analogues in isothermal and warm-up phase

TABLE 8Expected intensity ratio by assuming the same column density and rotational temperature

ratioEthanol

Methanol 0435

1minusPropanolMethanol 0181


MethanethiolMethanol 1163

EthanethiolMethanol 0249

1minusPropanethiolMethanol 0116


(for equilibrium structure as well as ground vibrational state) for 1-propanethiol and 2-propanethiol Here we haveemployed B3LYPaug-cc-pVTZ and HFcc-pVTZ method in Gaussian 09 program Aug prefix basis set is usedhere to mean that the basis set is augmented with diffusion function and cc-pVTZ is Dunning correlation consistentbasis sets (Kendall et al 1992) having triple zeta function This basis set has its redundant functions removedand is rotated (Davidson 1996) in order to increase computational efficiency Accuracy depends on the choice ofthe method and basis sets used Anharmonic vibrational-rotational coupling analysis is computed using the secondorder (numerical differentiation) perturbative anharmonic analysis Quartic rotation-vibration coupling is included inrotational parameters calculations Calculated rotational and distortional constants are shown in Table 6 to comparewith some existing results It is to be noted that the existing experimental results which are pointed out in Table 6


0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

Fig 4mdash Isotopic variation of infrared spectra of 1-propanethiol

were for the ground vibrational stateVarious components of dipole moments are computed for all the alcohols and their thiols considered in this study

In Table 7 we compare our calculated dipole moment components with the existing theoretical or experimentalresults Previous studies found that calculations at the HF level would predict dipole moment components close tothe experimental values Thus we use HF6-31g(d) level of theory for this computation It is expected that thesecomplex molecules could be detected in hot core regions Charnley et al (1995) pointed out that for an optically thinemission an idea about the antenna temperature could be made by calculating the intensity of a given transition

This intensity is proportional to micro2

Q(Trot) where micro is the electric dipole moment and Q(Trot) is the partition function

at rotational temperature Trot In Table 8 we compare the intensities for all the species with respect to methanolFor the computation of Q(Trot) we use

radicT 3(ABC) Rotational constants of these species are taken from earlier

studies (Takano et al 1968 Ohashi et al 1977 Hirota 1979 Sastry et al 1986 Lucia Herbst amp Anderson 1989 Kisielet al 2010 Muller et al 2015 Griffith amp Boggs 1975) Here we assume that all these species bear the same columndensity and rotational temperature Since we are aiming to study these molecules around hot core regions we are usingT = 180K for this calculation All these ratios are shown in Table 8 Very nice correlation is seen as we going to higherorder alcoholsthiols The spectral intensities along with the frequencies for rotational transitions of 1-propanethioland 2-propanethiol in the sub-millimeter regime are predicted by using quantum chemical calculations followed by theSPCAT program (Pickett 1991) For this calculations we use the experimentally obtained constants from Table 6 anduse experimentally obtained dipole moments from Table 7 We prepare this catalog files in JPL format and this filesare given as supplementary materials with this article

5 CONCLUSIONS

In this paper we study the formation of monohydric alcohols and their thiols Major highlights of our work are asfollows

bull In between various conformational isomers it is essential to find out the most stable conformer which might bea viable candidate for astronomical detections Here we carried out potential energy surface scan to find out themost stable isomer of the monohydric alcohols and their thiol analogues Among the alcohols methanol ethanoland 1-propanol have been claimed to be detected in the ISM whereas in thiols methanethiol and ethanethiol wereclaimed to be detected in hot core regions In between alcohols 2-propanol and in between thiols 1-propanethiol and2-propanethiol are yet to be detected in any sources Our calculations find that gauche Tg and trans conformer isthe most stable isomer for 2-propanol 1-propanethiol and 2-propanethiol respectively

12 Gorai et al

bull Reaction pathways in forming all stable isomers of monohydric alcohols and their thiols are prepared to study thechemical evolution

bull Our study reveals that around the warmer region (T gt 120 K) 1-propanethiol would be a viable candidate forastronomical detection in the gas phase

bull Since 1-propanethiol is yet to be detected in space we carried out quantum chemical calculation to study variousspectral aspects (in IR and sub-mm) of this species Band assignments were done for its various modes of vibrationChanges of absorbance spectra due to the isotopic effects were also pointed out Moreover we find out rotationaland distortional constants of this species and compare with existing experimental results Experimentally obtainedconstants and our calculated dipole moment components are further utilized to predict various probable transitionswhich should be useful for the future detection of this species in the ISM

6 ACKNOWLEDGEMENT

PG is grateful to DST (Grant No SBS2HEP-0212013) for the partial financial support AD and SKC want toacknowledge ISRO respond project (Grant No ISRORES240216-17) EEE acknowledges a research fellowshipfrom the Indian Institute of Science Bangalore Amaresh Das acknowledges the partial support of Inidian Centre forSpace Physics

REFERENCES

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Allen M amp Robinson G W 1977 ApJ 212 396Abdurakhmanov A A Ragimova R A amp Imanov L M

1970 PhL 32A 123Abdurakhmanov A A amp Ismailzade G I 1984 Zh

Strukturnoi Khimii 1987 28 91 ( English transl in J StructChem 28 238)

Biham O Furman I Pirronello V amp Vidali G 2001 ApJ553 595

Becke A D 1988 PhRvA 386 3098Boogert A C A Schutte W A Helmich F P Tielens A G

G M amp Wooden D H 1997 AampA 317 929Cazaux S Cobut V Marseille M Spaans M amp Caselli P

2010 AampA 522 74Caselli P Stantcheva T Shalabiea O Shematovich V I amp

Herbst E 2002 PampSS50 1257Chakrabarti S K Das A Acharyya K amp Chakrabarti S

2006 AampA 457 167Chakrabarti S K Das A Acharyya K amp Chakrabarti S

2006 BASI 34 299Chakrabarti S K Majumdar S K Das A amp Chakrabarti S

2015 ApampSS 357 90Choi S Kang T T Choi K W Han S Ahn D S Baek S

J amp Kim S K 2008 JPhCh A 112 7191Cuppen H amp Herbst E 2007 ApJ 668 294Charnley S B Kress M E Tielens A G G M amp Millar T

J 1995 ApJ 448 232Das A Chakrabarti S K Acharyya K amp Chakrabarti S

2008b NewA 13 457Das A Acharyya K Chakrabarti S amp Chakrabarti S K

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789Das A amp Chakrabarti S K 2011 418 545 MNRASDas A Majumdar L Chakrabarti S K amp Chakrabarti S

2013a NewA 23 118Das A Majumdar L Chakrabarti S K Saha R amp

Chakrabarti S 2013b MNRAS 433 3152Das A Majumdar L Chakrabarti S K amp Sahu D 2015a

NewA 35 53Das A Majumdar L Sahu D Gorai P Sivaraman B amp

Chakrabarti S K 2015b ApJ 808 21Das A Sahu D Majumdar L amp Chakrabarti S K 2016

MNRAS 455 540Davidson E R CPL 1996 260 514-18Druard C amp Wakelam V 2012 MNRAS 426 354Ferrante R F Moore M H Spiliotis M M amp Hudson R L

2008 ApJ 684 1210Foresman JB amp Frisch A 1995-96 Exploring Chemistry with

Electronic structure Gaussian Inc Pittsburgh PA 15106USA

Frisch M J et al 2009 Ins Wallingford CT Gaussian 09Revision E01

Garrod RT amp Herbst E 2006 AampA 457 927Garrod R T 2013 ApJ 765 60Garozzo M Fulvio D Kanuchova Z Palumbo M E amp

Strazzulla G 2010 AampA 509 A67Gibb E L Whittet D C B Boogert A C A amp Tielens A

G G M 2004 ApJS 151 35Griffith J H amp Boggs J E 1975 JMoSp 56 257Hasegawa T amp Herbst E 1993 MNRAS 261 83Hasegawa T Herbst E amp Leung C M 1992 ApJ 82 167Howk J C Sembach K R amp Savage B D 2006 ApJ 637

333Hirota E 1979a JPhCh 83 1457Hirota E 1979 JPhCh 83 1457Ivash E V amp Dennison D M 1953 JChPh 21 1804Jansen D J Spaans M Hogerheijde M R amp van Dishoeck

E F 1995 AampA 303 541Johansson L E B Andersson C Ellder J et al 1984 AampA

130 227Kendall R A Dunning JrT H amp Harrison R J JChPh

1992 96Kisiel Z Dorosh O Maeda A et al 2010 Phys Chem Chem

Phys 12 8329Kolesnikova L Tercero B Cernicharo J et al 2014 ApJ 784

L7Leung CM Herbst E amp Huebner WF 1984 ApJS 56 231Lide D R 2001 CRC Handbook of Chemistry and Physics

82th ed CRC Press Boca Raton FL Section 10Lotta T Murto J Rasanen M amp Aspala A 1984 Chem

Phys 86 105Lee C Yang W amp Parr R G 1988 PhRvB 58 785Linke R A Frerking M A amp Thaddeus P 1979 ApJ 234

L139Lucia F C D Herbst E amp Anderson T 1989 JMoSp 134

395Maeda A Lucia F C D Herbst E et al 2006 ApJ 162 428Majumdar L Das A amp Chakrabarti S K 2014a AampA 562

A56Majumdar L Das A amp Chakrabarti S K 2014b ApJ 782 73Majumdar L Das A Chakrabarti S K amp Chakrabarti S

2013 New Astronomy 20 15Majumdar L Das A Chakrabarti S K amp Chakrabarti S

2012 RAA 12 1613Majumdar L Gratier P Vidal T Wakelam V Loison J C

Hickson K M amp Caux E 2016 MNRAS 458 1859Millar T J amp Herbst E 1990 AampA 231 466Millar TJ Olofsson H Hjalmarson A Brown PD 1988

AampA 205 L5Muller H S P Belloche A Xu Li-Hong et al AampA 2015Ohashi O Ohnishi M Tagui A Sakaizumi T amp Yamaguchi

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Palumbo M E Tielens A G G M amp Tokunaga A T 1995ApJ 449 674

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Paul M Woods A Occhiogrosso S Viti Z Kanuchov a ME Palumbo amp S D Pric 2014 MNRAS 000 1

Peterson K A amp Dunning T H 2002 JChPh 117 10548Pickett H M JMoSp 1991 148 371Quan D Herbst E Corby J Durr A amp Hassel G 2016

ApJ 824 129Requena-Torres M A Martin-Pintado J Martin S amp Morris

M R ApJ 2008 672 352Sahu D Das A Majumdar L amp Chakrabarti S K 2015

NewA 38 23Scappini F Cecchi-Pestellini C Smith H Klemperer W amp

Dalgarno A 2003 MNRAS 341 657Swings P amp Rosenfeld L ApJ 1937 86 483SSavage B D amp Sembach K R 1996 ARAampA 34 279Sastry K V L N Herbst E Booker A R amp Lucia F C D

1986 JMoSp 116 120-135Schmidt R E amp Quade C R 1975 JChPh 62 3864Smith D Devlin J P amp Scott D W 1968 JMoSp 25 174-184Sofia U J Cardelli J A amp Savage B D 1994 ApJ 430 650

Takano M Sasada Y amp Satoh T 1968 JMoSp 26 157-162Tielens A G G M Allamandola L J 1987b In Hollenbach

D J amp Thronson HA 1987 (Eds) Interstellar ProcessKluwer Dordrecht p 397

Tercero B Cernicharo J amp Lopez et al 2015 AampA 582 L1Tielens A G G M amp Allamandola L J 1987a in physical

process in interstellar clouds ed N Kaifu (Tokyo Univ TokyoPress) 237

Tsunekawa S Taniguchi I Tambo A et al 1989 JMoSp 13463

Tieftrunk A Pineau des Forets G Schilke P amp Walmsley CM 1994 AampA 289 579

Torgrimsen T Klaeboe P et al 1970 Acta ChemicaScandinavica 24 1139-1144

Turner B E 1991 ApJs 76 617Turner B E 1977 ApJ 213 L75Woods P M Occhiogrosso A Viti S Kauchov Z Palumbo

M E amp Price S D 2015 MNRAS 450 1256Woodall J Agndez M Markwick-Kemper A J amp Millar T

J 2007 AampA 466 1197

ABSTRACT

1 Introduction

2 Search for most stable conformational isomers





3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement

2 Gorai et al

claim had been confirmed by Linke et al (1979) and showed that CH3SHCH3OH ratio is close to the cosmic SOratio Recently Majumdar et al (2016) detected CH3SH in IRAS 16293-2422 and Kolesnikova et al (2014) reportedthe detection of C2H5SH in hot core Orion KL But very recent observation by Muller et al (2015) suggested that thedetection of C2H5SH in Orion KL is uncertain Presence of higher order thiols are yet to be seen

In this paper we discuss the formation of monohydric alcohols and their thiol analogues First we identify the moststable conformer of alcohols and their thiols Then we develop a chemical network to study the formation of all thesespecies From the outcome of our chemical modeling most probable new candidate for the astronomical detectionis found out Moreover a detailed spectroscopic study is carried out to set a guideline for observing this species innear future This paper is organized as follows Section 2 describes the quantum chemical calculation to find outthe most stable conformers Section 3 contains chemical modeling Section 4 contains the information regarding thespectroscopic parameters for the detection of the next probable candidate Finally in Section 5 we make concludingremarks

2 SEARCH FOR MOST STABLE CONFORMATIONAL ISOMERS

All the quantum chemical calculations reported here are calculated by using Gaussian 09 program (Frisch et al 2009Foresman amp Frisch 1996) Each optimized structure is verified by avoiding the imaginary frequency With the advanceof quantum chemical calculation a proper choice of Method and basis sets are required to compute the molecularproperties

According to IUPAC definition of a conformer conformational isomerism is a form of stereo isomerism in whichthe isomers can be inter-converted exclusively by rotations about formally single bonds It is expected that the moststable conformer would be the most probable candidate for the astronomical detection In this attempt here beforeconstructing our chemical model we search for the various conformers of the monohydric alcohols and their thiolsthrough relaxed potential energy surface (PES) scan of dihedral angles PES scan results are displayed in Fig 1and relative energies of the conformers are pointed out in Table 1 2-propanol2-propanethiol is the structural isomerof 1-propanol1-propanethiol for the sake of completeness we discuss about their conformers as well For all thesecalculation we use Moslashller-Plesset perturbation theory (MP2) with the Peterson and Dunningrsquos correlation consistentbasis set (cc-pVTZ) (Peterson amp Dunning 2002) of Gaussian 09 software Results of the PES scans are the following


Methanol and methanethiol both show internal rotation of CH3 group From relaxed potential energy surface scan(minus180 to +180 of dihedral angle ang(H3C1O6H5)) we have shown that methanol and methanethiol both exist inthe most stable state at plusmn 180 of the dihedral angle on PES On the other hand there exist three different maximafor both methanol and methanethiol at plusmn 120 and at 0 Relative energies are pointed out in Table 1


In case of ethanol and ethanethiol both have two types of internal rotation around OHSH group and CH3 groupDue to internal rotation of the OHSH group of ethanolethanethiol it may exist in four different forms For ethanoltransanti conformation (dihedral angle ang(C1C5O8H9) =180) is the minimum energy state on PES The gaucheconformer (dihedral angle ang(C1C5O8H9) = plusmn60) is situated slightly upper on the PES The relative energy betweenthe trans and gauche conformer is 0877 cmminus1 When the dihedral angle is plusmn 120 conformers are called eclipsedThe relative energy between trans and eclipsed conformer is 415 cmminus1 When the dihedral angle is 0 it is called cisconformer which is also situated at higher energy state on the PES The relative energy between trans and cis conformeris 456 cmminus1 (13 Kcalmol) Whereas for ethanethiol the most stable conformer is gauche in which ang(C1C5S8H9)dihedral angle is at plusmn 60 Relative energy between gauche and trans conformer is 170 cmminus1 (049 Kcalmol) relativeenergy between gauche and eclipsed conformer is 524 cmminus1 (150 Kcalmol) and the relative energy between gaucheand cis conformer is 541 cmminus1 (155 Kcalmol) Due to CH3 rotation there would also be some changes in the energybetween the conformers but all are higher as compared to the most stable one


Maeda et al (2006) discussed five possible conformational isomers of 1-propanol originating from alternate structureof the central (C1C5O8H9) and (O8C5C1H3) skeletal chains These five forms are Transminus trans (Tt) T ransminusgauche (Tg) Gauche minus trans (Gt) Gauche minus gauche (Gg) and Gauche minus gauche

prime(Gg

prime) Based on the relative

energies of these conformers Abdurakhmanov amp Ismailzade (1987) find out that Tg conformer has the lowest energyHowever Lotta et al (1984) Kisiel et al (2010) predicted that Gt conformer has the lowest energy Our quantumchemical study also finds that Gt conformer has the lowest energy As in earlier studies in terms of their relativeenergies we found that 1-propanol conformer follows the sequence of Gt Gg

prime Gg Tg T t in the ascending order of

relative energiesSimilar studies have been carried out for 1-propanethiol Since 1-propanethiol is yet to be detected in the ISM

perspective views of its five possible staggered conformers originating from the combination of trans and gaucheconfiguration is shown in Fig 2 Our calculation reveals that Tg configuration has the lowest energies Relativeenergies of all the conformers with respect to the Tg conformer are shown in Table 1


0

05

1

15

-200 -100 0 100 200

Dihedral angle

-05

0

05

1

15

Ene

rgy

(in K

calm

ol)

Methanol

Methanethiol

-1

0

1

-200 -100 0 100 200

Dihedral angle

-2

0

2

4

-100 0 100 200

Dihedral angle

Ethanol

Ene

rgy

(in K

calm

ol) Ethanethiol

Ethanol

Ethanethiol

C1-C5-O8-H9

C1-C5-S8-H9

O8-C5-C1-H3

S8-C5-C1-H3

-3

-2

-1

0

1

2

-200 -100 0 100 200

Dihedral angle

0

1

-100 0 100 200

Dihedral angle

1-propanol

Ene

rgy

(in K

calm

ol)

1-propanethiol

1-propanol

1-propanethiol

C1-C5-O8-H9

C1-C5-S8-H9

O8-C5-C1-H3

S8-C5-C1-H3

-05

0

05

1

15

2

-200 -100 0 100 200

Dihedral angle

-05

0

05

1

15

2

Ene

rgy

(in K

calm

ol)

2-Propanol

2-Propanethiol


4 Gorai et al




HCOH plusmn 60 04389 (00013)


HCOH 0 395 (113)


HCSH plusmn 60 0877 (00025)


HCSH 0 445 (127)

trans 0 (0)

gauche 23 (0066)


cis 456 (130)

gauche CCSH 0 (0)



cis 541 (155)

Gt 0 (0)

Gg 67 (019)

1-propanol Ggprime

35 (001)

Tt 95 (027)

Tg 80 (023)

Tg 0 (0)

Tt 216 (062)


Ggprime

63 (018)

Gg 46 (013)

gauche 0 (0)


trans 0 (0)





3 CHEMICAL MODELING




Methanol











Methanethiol




S + CH3 rarr CH3S 0






Ethanol





Ethanethiol



























31 Chemical network



6 Gorai et al












CH3OHC2H5OH

2663 1879 324 45t78m1

CH3OHCH3CH2CH2OH

208 times 109 3485 779 2700t

C2H5OHCH3CH2CH2OH

773843 185 240 60t

CH3SHC2H5SH

261 times 1011 708 455 ge 21m31m1

CH3OHCH3SH

269 3443 1127 120m 5700m1

C2H5OHC2H5SH

262 times 108 129 157 125m225m1










33 Modeling results







4 SPECTROSCOPY



8 Gorai et al


basis set







































































Ae 24213642(2442975) ∆J 0296911(0208512)

Be 2312864( 233788) ∆K 21457798(6184248)

Ce 2222041( 224540) ∆JK 29811(422776)

δ1 -00455(-0039844)

A0 2323981( 2363275) 234290 δ2 04518(996033)








Ae 7886965( 793821) ∆J 1246( 1043)

Be 4341565( 439957) ∆K 6799(5473)

Ce 3118889( 315254) DJK 2184(3312)

δ1 3728(0265)

A0 778214(784142) 789265 δ2 03805(1933)









bracket



Methanol -15406 (144a) 10537 (0899a) 00 18665 (169a)



Ethanethiol 00431(106d) 18597(117d) 000 18602 (150d)









12CH232SH


13CH232SH)



10 Gorai et al

1e+03 1e+04 1e+05 1e+06

log (time) year

1e-25

1e-20

1e-15

1e-10

1e-05

log

(a

bu

nd

an

ce)

Methanol (gas)

Ethanol (gas)

Propanol (gas)

Methanethiol (gas)

Ethanethiol (gas)

Propanethiol (gas)

Methanol (ice)

Ethanol (ice)

Propanol (ice)

Methanethiol (ice)

Ethanethiol (ice)

Propanethiol (ice)

10e+06 12e+06 14e+06 16e+06 18e+06 20e+06

Time (year)

1e-14

1e-12

1e-10

1e-08

1e-06

1e-04

log

(a

bu

nd

an

ce)

480 860 1240 1620 2000

Temperature (K)

Isothermal phase

Warm-up phase



ratioEthanol

Methanol 0435









0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH









5 CONCLUSIONS



12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement


0

05

1

15

-200 -100 0 100 200

Dihedral angle

-05

0

05

1

15

Ene

rgy

(in K

calm

ol)

Methanol

Methanethiol

-1

0

1

-200 -100 0 100 200

Dihedral angle

-2

0

2

4

-100 0 100 200

Dihedral angle

Ethanol

Ene

rgy

(in K

calm

ol) Ethanethiol

Ethanol

Ethanethiol

C1-C5-O8-H9

C1-C5-S8-H9

O8-C5-C1-H3

S8-C5-C1-H3

-3

-2

-1

0

1

2

-200 -100 0 100 200

Dihedral angle

0

1

-100 0 100 200

Dihedral angle

1-propanol

Ene

rgy

(in K

calm

ol)

1-propanethiol

1-propanol

1-propanethiol

C1-C5-O8-H9

C1-C5-S8-H9

O8-C5-C1-H3

S8-C5-C1-H3

-05

0

05

1

15

2

-200 -100 0 100 200

Dihedral angle

-05

0

05

1

15

2

Ene

rgy

(in K

calm

ol)

2-Propanol

2-Propanethiol


4 Gorai et al




HCOH plusmn 60 04389 (00013)


HCOH 0 395 (113)


HCSH plusmn 60 0877 (00025)


HCSH 0 445 (127)

trans 0 (0)

gauche 23 (0066)


cis 456 (130)

gauche CCSH 0 (0)



cis 541 (155)

Gt 0 (0)

Gg 67 (019)

1-propanol Ggprime

35 (001)

Tt 95 (027)

Tg 80 (023)

Tg 0 (0)

Tt 216 (062)


Ggprime

63 (018)

Gg 46 (013)

gauche 0 (0)


trans 0 (0)





3 CHEMICAL MODELING




Methanol











Methanethiol




S + CH3 rarr CH3S 0






Ethanol





Ethanethiol



























31 Chemical network



6 Gorai et al












CH3OHC2H5OH

2663 1879 324 45t78m1

CH3OHCH3CH2CH2OH

208 times 109 3485 779 2700t

C2H5OHCH3CH2CH2OH

773843 185 240 60t

CH3SHC2H5SH

261 times 1011 708 455 ge 21m31m1

CH3OHCH3SH

269 3443 1127 120m 5700m1

C2H5OHC2H5SH

262 times 108 129 157 125m225m1










33 Modeling results







4 SPECTROSCOPY



8 Gorai et al


basis set







































































Ae 24213642(2442975) ∆J 0296911(0208512)

Be 2312864( 233788) ∆K 21457798(6184248)

Ce 2222041( 224540) ∆JK 29811(422776)

δ1 -00455(-0039844)

A0 2323981( 2363275) 234290 δ2 04518(996033)








Ae 7886965( 793821) ∆J 1246( 1043)

Be 4341565( 439957) ∆K 6799(5473)

Ce 3118889( 315254) DJK 2184(3312)

δ1 3728(0265)

A0 778214(784142) 789265 δ2 03805(1933)









bracket



Methanol -15406 (144a) 10537 (0899a) 00 18665 (169a)



Ethanethiol 00431(106d) 18597(117d) 000 18602 (150d)









12CH232SH


13CH232SH)



10 Gorai et al

1e+03 1e+04 1e+05 1e+06

log (time) year

1e-25

1e-20

1e-15

1e-10

1e-05

log

(a

bu

nd

an

ce)

Methanol (gas)

Ethanol (gas)

Propanol (gas)

Methanethiol (gas)

Ethanethiol (gas)

Propanethiol (gas)

Methanol (ice)

Ethanol (ice)

Propanol (ice)

Methanethiol (ice)

Ethanethiol (ice)

Propanethiol (ice)

10e+06 12e+06 14e+06 16e+06 18e+06 20e+06

Time (year)

1e-14

1e-12

1e-10

1e-08

1e-06

1e-04

log

(a

bu

nd

an

ce)

480 860 1240 1620 2000

Temperature (K)

Isothermal phase

Warm-up phase



ratioEthanol

Methanol 0435









0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH









5 CONCLUSIONS



12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement

4 Gorai et al




HCOH plusmn 60 04389 (00013)


HCOH 0 395 (113)


HCSH plusmn 60 0877 (00025)


HCSH 0 445 (127)

trans 0 (0)

gauche 23 (0066)


cis 456 (130)

gauche CCSH 0 (0)



cis 541 (155)

Gt 0 (0)

Gg 67 (019)

1-propanol Ggprime

35 (001)

Tt 95 (027)

Tg 80 (023)

Tg 0 (0)

Tt 216 (062)


Ggprime

63 (018)

Gg 46 (013)

gauche 0 (0)


trans 0 (0)





3 CHEMICAL MODELING




Methanol











Methanethiol




S + CH3 rarr CH3S 0






Ethanol





Ethanethiol



























31 Chemical network



6 Gorai et al












CH3OHC2H5OH

2663 1879 324 45t78m1

CH3OHCH3CH2CH2OH

208 times 109 3485 779 2700t

C2H5OHCH3CH2CH2OH

773843 185 240 60t

CH3SHC2H5SH

261 times 1011 708 455 ge 21m31m1

CH3OHCH3SH

269 3443 1127 120m 5700m1

C2H5OHC2H5SH

262 times 108 129 157 125m225m1










33 Modeling results







4 SPECTROSCOPY



8 Gorai et al


basis set







































































Ae 24213642(2442975) ∆J 0296911(0208512)

Be 2312864( 233788) ∆K 21457798(6184248)

Ce 2222041( 224540) ∆JK 29811(422776)

δ1 -00455(-0039844)

A0 2323981( 2363275) 234290 δ2 04518(996033)








Ae 7886965( 793821) ∆J 1246( 1043)

Be 4341565( 439957) ∆K 6799(5473)

Ce 3118889( 315254) DJK 2184(3312)

δ1 3728(0265)

A0 778214(784142) 789265 δ2 03805(1933)









bracket



Methanol -15406 (144a) 10537 (0899a) 00 18665 (169a)



Ethanethiol 00431(106d) 18597(117d) 000 18602 (150d)









12CH232SH


13CH232SH)



10 Gorai et al

1e+03 1e+04 1e+05 1e+06

log (time) year

1e-25

1e-20

1e-15

1e-10

1e-05

log

(a

bu

nd

an

ce)

Methanol (gas)

Ethanol (gas)

Propanol (gas)

Methanethiol (gas)

Ethanethiol (gas)

Propanethiol (gas)

Methanol (ice)

Ethanol (ice)

Propanol (ice)

Methanethiol (ice)

Ethanethiol (ice)

Propanethiol (ice)

10e+06 12e+06 14e+06 16e+06 18e+06 20e+06

Time (year)

1e-14

1e-12

1e-10

1e-08

1e-06

1e-04

log

(a

bu

nd

an

ce)

480 860 1240 1620 2000

Temperature (K)

Isothermal phase

Warm-up phase



ratioEthanol

Methanol 0435









0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH









5 CONCLUSIONS



12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement




Methanol











Methanethiol




S + CH3 rarr CH3S 0






Ethanol





Ethanethiol



























31 Chemical network



6 Gorai et al












CH3OHC2H5OH

2663 1879 324 45t78m1

CH3OHCH3CH2CH2OH

208 times 109 3485 779 2700t

C2H5OHCH3CH2CH2OH

773843 185 240 60t

CH3SHC2H5SH

261 times 1011 708 455 ge 21m31m1

CH3OHCH3SH

269 3443 1127 120m 5700m1

C2H5OHC2H5SH

262 times 108 129 157 125m225m1










33 Modeling results







4 SPECTROSCOPY



8 Gorai et al


basis set







































































Ae 24213642(2442975) ∆J 0296911(0208512)

Be 2312864( 233788) ∆K 21457798(6184248)

Ce 2222041( 224540) ∆JK 29811(422776)

δ1 -00455(-0039844)

A0 2323981( 2363275) 234290 δ2 04518(996033)








Ae 7886965( 793821) ∆J 1246( 1043)

Be 4341565( 439957) ∆K 6799(5473)

Ce 3118889( 315254) DJK 2184(3312)

δ1 3728(0265)

A0 778214(784142) 789265 δ2 03805(1933)









bracket



Methanol -15406 (144a) 10537 (0899a) 00 18665 (169a)



Ethanethiol 00431(106d) 18597(117d) 000 18602 (150d)









12CH232SH


13CH232SH)



10 Gorai et al

1e+03 1e+04 1e+05 1e+06

log (time) year

1e-25

1e-20

1e-15

1e-10

1e-05

log

(a

bu

nd

an

ce)

Methanol (gas)

Ethanol (gas)

Propanol (gas)

Methanethiol (gas)

Ethanethiol (gas)

Propanethiol (gas)

Methanol (ice)

Ethanol (ice)

Propanol (ice)

Methanethiol (ice)

Ethanethiol (ice)

Propanethiol (ice)

10e+06 12e+06 14e+06 16e+06 18e+06 20e+06

Time (year)

1e-14

1e-12

1e-10

1e-08

1e-06

1e-04

log

(a

bu

nd

an

ce)

480 860 1240 1620 2000

Temperature (K)

Isothermal phase

Warm-up phase



ratioEthanol

Methanol 0435









0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH









5 CONCLUSIONS



12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement

6 Gorai et al












CH3OHC2H5OH

2663 1879 324 45t78m1

CH3OHCH3CH2CH2OH

208 times 109 3485 779 2700t

C2H5OHCH3CH2CH2OH

773843 185 240 60t

CH3SHC2H5SH

261 times 1011 708 455 ge 21m31m1

CH3OHCH3SH

269 3443 1127 120m 5700m1

C2H5OHC2H5SH

262 times 108 129 157 125m225m1










33 Modeling results







4 SPECTROSCOPY



8 Gorai et al


basis set







































































Ae 24213642(2442975) ∆J 0296911(0208512)

Be 2312864( 233788) ∆K 21457798(6184248)

Ce 2222041( 224540) ∆JK 29811(422776)

δ1 -00455(-0039844)

A0 2323981( 2363275) 234290 δ2 04518(996033)








Ae 7886965( 793821) ∆J 1246( 1043)

Be 4341565( 439957) ∆K 6799(5473)

Ce 3118889( 315254) DJK 2184(3312)

δ1 3728(0265)

A0 778214(784142) 789265 δ2 03805(1933)









bracket



Methanol -15406 (144a) 10537 (0899a) 00 18665 (169a)



Ethanethiol 00431(106d) 18597(117d) 000 18602 (150d)









12CH232SH


13CH232SH)



10 Gorai et al

1e+03 1e+04 1e+05 1e+06

log (time) year

1e-25

1e-20

1e-15

1e-10

1e-05

log

(a

bu

nd

an

ce)

Methanol (gas)

Ethanol (gas)

Propanol (gas)

Methanethiol (gas)

Ethanethiol (gas)

Propanethiol (gas)

Methanol (ice)

Ethanol (ice)

Propanol (ice)

Methanethiol (ice)

Ethanethiol (ice)

Propanethiol (ice)

10e+06 12e+06 14e+06 16e+06 18e+06 20e+06

Time (year)

1e-14

1e-12

1e-10

1e-08

1e-06

1e-04

log

(a

bu

nd

an

ce)

480 860 1240 1620 2000

Temperature (K)

Isothermal phase

Warm-up phase



ratioEthanol

Methanol 0435









0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH









5 CONCLUSIONS



12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement



33 Modeling results







4 SPECTROSCOPY



8 Gorai et al


basis set







































































Ae 24213642(2442975) ∆J 0296911(0208512)

Be 2312864( 233788) ∆K 21457798(6184248)

Ce 2222041( 224540) ∆JK 29811(422776)

δ1 -00455(-0039844)

A0 2323981( 2363275) 234290 δ2 04518(996033)








Ae 7886965( 793821) ∆J 1246( 1043)

Be 4341565( 439957) ∆K 6799(5473)

Ce 3118889( 315254) DJK 2184(3312)

δ1 3728(0265)

A0 778214(784142) 789265 δ2 03805(1933)









bracket



Methanol -15406 (144a) 10537 (0899a) 00 18665 (169a)



Ethanethiol 00431(106d) 18597(117d) 000 18602 (150d)









12CH232SH


13CH232SH)



10 Gorai et al

1e+03 1e+04 1e+05 1e+06

log (time) year

1e-25

1e-20

1e-15

1e-10

1e-05

log

(a

bu

nd

an

ce)

Methanol (gas)

Ethanol (gas)

Propanol (gas)

Methanethiol (gas)

Ethanethiol (gas)

Propanethiol (gas)

Methanol (ice)

Ethanol (ice)

Propanol (ice)

Methanethiol (ice)

Ethanethiol (ice)

Propanethiol (ice)

10e+06 12e+06 14e+06 16e+06 18e+06 20e+06

Time (year)

1e-14

1e-12

1e-10

1e-08

1e-06

1e-04

log

(a

bu

nd

an

ce)

480 860 1240 1620 2000

Temperature (K)

Isothermal phase

Warm-up phase



ratioEthanol

Methanol 0435









0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH









5 CONCLUSIONS



12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement

8 Gorai et al


basis set







































































Ae 24213642(2442975) ∆J 0296911(0208512)

Be 2312864( 233788) ∆K 21457798(6184248)

Ce 2222041( 224540) ∆JK 29811(422776)

δ1 -00455(-0039844)

A0 2323981( 2363275) 234290 δ2 04518(996033)








Ae 7886965( 793821) ∆J 1246( 1043)

Be 4341565( 439957) ∆K 6799(5473)

Ce 3118889( 315254) DJK 2184(3312)

δ1 3728(0265)

A0 778214(784142) 789265 δ2 03805(1933)









bracket



Methanol -15406 (144a) 10537 (0899a) 00 18665 (169a)



Ethanethiol 00431(106d) 18597(117d) 000 18602 (150d)









12CH232SH


13CH232SH)



10 Gorai et al

1e+03 1e+04 1e+05 1e+06

log (time) year

1e-25

1e-20

1e-15

1e-10

1e-05

log

(a

bu

nd

an

ce)

Methanol (gas)

Ethanol (gas)

Propanol (gas)

Methanethiol (gas)

Ethanethiol (gas)

Propanethiol (gas)

Methanol (ice)

Ethanol (ice)

Propanol (ice)

Methanethiol (ice)

Ethanethiol (ice)

Propanethiol (ice)

10e+06 12e+06 14e+06 16e+06 18e+06 20e+06

Time (year)

1e-14

1e-12

1e-10

1e-08

1e-06

1e-04

log

(a

bu

nd

an

ce)

480 860 1240 1620 2000

Temperature (K)

Isothermal phase

Warm-up phase



ratioEthanol

Methanol 0435









0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH









5 CONCLUSIONS



12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement








Ae 24213642(2442975) ∆J 0296911(0208512)

Be 2312864( 233788) ∆K 21457798(6184248)

Ce 2222041( 224540) ∆JK 29811(422776)

δ1 -00455(-0039844)

A0 2323981( 2363275) 234290 δ2 04518(996033)








Ae 7886965( 793821) ∆J 1246( 1043)

Be 4341565( 439957) ∆K 6799(5473)

Ce 3118889( 315254) DJK 2184(3312)

δ1 3728(0265)

A0 778214(784142) 789265 δ2 03805(1933)









bracket



Methanol -15406 (144a) 10537 (0899a) 00 18665 (169a)



Ethanethiol 00431(106d) 18597(117d) 000 18602 (150d)









12CH232SH


13CH232SH)



10 Gorai et al

1e+03 1e+04 1e+05 1e+06

log (time) year

1e-25

1e-20

1e-15

1e-10

1e-05

log

(a

bu

nd

an

ce)

Methanol (gas)

Ethanol (gas)

Propanol (gas)

Methanethiol (gas)

Ethanethiol (gas)

Propanethiol (gas)

Methanol (ice)

Ethanol (ice)

Propanol (ice)

Methanethiol (ice)

Ethanethiol (ice)

Propanethiol (ice)

10e+06 12e+06 14e+06 16e+06 18e+06 20e+06

Time (year)

1e-14

1e-12

1e-10

1e-08

1e-06

1e-04

log

(a

bu

nd

an

ce)

480 860 1240 1620 2000

Temperature (K)

Isothermal phase

Warm-up phase



ratioEthanol

Methanol 0435









0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH









5 CONCLUSIONS



12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement

10 Gorai et al

1e+03 1e+04 1e+05 1e+06

log (time) year

1e-25

1e-20

1e-15

1e-10

1e-05

log

(a

bu

nd

an

ce)

Methanol (gas)

Ethanol (gas)

Propanol (gas)

Methanethiol (gas)

Ethanethiol (gas)

Propanethiol (gas)

Methanol (ice)

Ethanol (ice)

Propanol (ice)

Methanethiol (ice)

Ethanethiol (ice)

Propanethiol (ice)

10e+06 12e+06 14e+06 16e+06 18e+06 20e+06

Time (year)

1e-14

1e-12

1e-10

1e-08

1e-06

1e-04

log

(a

bu

nd

an

ce)

480 860 1240 1620 2000

Temperature (K)

Isothermal phase

Warm-up phase



ratioEthanol

Methanol 0435









0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH









5 CONCLUSIONS



12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement


0

50

100

150

200

250

300

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000 3500 4000

Wavenumber (cm-1

)

0

50

100

150

200

250

300

0

50

100

150

0

50

100

150

0

100

200

300

0

100

200

300

0

25

50

0

25

50

0

25

50

CH3CH

2

12H

2

34SH

CH3CH

2

13CH

2

34SH

CH3CH

2

13CH

2

32SH

Ab

so

rb

an

ce (

Km

mo

l)

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH

CH3CH

2

12CH

2

32SH









5 CONCLUSIONS



12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement

12 Gorai et al




6 ACKNOWLEDGEMENT


REFERENCES
































































J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement




















J 2007 AampA 466 1197

ABSTRACT

1 Introduction






3 Chemical modeling

31 Chemical network


33 Modeling results

4 Spectroscopy



5 Conclusions

6 Acknowledgement

arxiv:1612.02688v1 [astro-ph.ga] 8 dec 2016

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