microwave spectroscopy of seven conformers of 1,2-propanediol
DESCRIPTION
Centers for Chemical Innovation. Microwave Spectroscopy of Seven Conformers of 1,2-Propanediol. Justin L. Neill , Matt T. Muckle, and Brooks H. Pate , Department of Chemistry, University of Virginia F. J. Lovas, D. F. Plusquellic, Optical Technology Division, NIST - PowerPoint PPT PresentationTRANSCRIPT
Microwave Spectroscopy of Seven Conformers of 1,2-Propanediol
Justin L. Neill, Matt T. Muckle, and Brooks H. Pate, Department of Chemistry, University of Virginia
F. J. Lovas, D. F. Plusquellic, Optical TechnologyDivision, NIST
A. J. Remijan, National Radio Astronomy Observatory
Centers for Chemical Innovation
Conformers of 1,2-propanediol: mp2/aug-cc-pVTZO
2-C
3-C
4-C
7 dihedral = 180º O
2-C
3-C
4-C
7 dihedral = 60º
O2 is
H-bondacceptor
O2 is
H-bonddonor
conf. 1E = 192 cm-1
conf. 2E = 83 cm-1
conf. 3E = 0 cm-1
conf. 5E = 87 cm-1
conf. 4E = 338 cm-1
conf. 6E = 213 cm-1
conf. 7E = 345 cm-1
conf. 8E = 441 cm-1
Detected by CaminatiaDetected by Caminatia
Detected by Lockley et alb
aW. Caminati, J. Mol. Spectrosc. 86 (1981) 193-201. bT.J.L. Lockley et al., J. Mol. Struct. 612 (2002) 199-206.
New MeasurementsTwo spectrometers employed:
1) Balle-Flygare-type FTMW spectrometer at NISTa
discovered conformer 4Stark effect measurements (conformers 1-3)high-resolution measurements (all conformers) for final fits
2) Chirped-pulse FTMW spectrometer at UVab operating between 6.5-18.5 GHz—288,000 averaged FIDs
aF.J. Lovas and R.D. Suenram, J. Chem. Phys. 87 (1987) 2010-2020.bG.G. Brown, B.C. Dian, K.O. Douglass, S.M. Geyer, S.T. Shipman, and B.H. Pate, Rev. Sci. Instrum.
79 (2008) 53103-1-13.
Sample (mix of enantiomers) purchased from Aldrich (>99.5%, <0.2% H
2O); internal reservoir, heated to 60ºC
(CP-FTMW: strongest (H2O)2 line factor of 3,000 downfrom strongest 1,2-propanediol line)
CP-FTMW Modifications 2008-09-24 GS/s AWG (Tektronix AWG7122B); more accurate intensities over full spectral range-50 GS/s oscilloscope (Tektronix DPO71022); all signals directly digitized
(no peaks due to mixing bleedthroughs)-Sample conservation techniques: 2 nozzles, 10 FIDs per gas pulse-nozzle slowed to 0.6 Hz (limited by oscilloscope's data processing speed) at a 20 μs
FID length (10,000,000 points collected per valve pulse) 21,000 FIDs collectedper hour of averaging—14 hours to collect 288k average spectrum
-limited by oscilloscope processing speed—potential factor of 16 enhancement
Other talks using UVa CP-FTMW:MH08—propofol (A.Lesarri)TA05—strawberry aldehyde (S.Shipman)TA09—chloropentafluorobenzene (A.Osthoff)WI06—isomers of HSCN in electric discharge
(M.McCarthy)RC11—p-methoxyphenethylamine—water
(J.Neill)RH08—diethylsilane (A.Steber)trans-methyl formate (M.Muckle)
CP-FTMW Modifications 2008-09FastFrame
Arbitrary waveform generator puts out 10-MW pulse chain (with 25 µs buffer between pulses)
Oscilloscope saves spectrum every ~2.5 h (in case of power outages, phase shifts)
Puts greater stress on passive diode limiter (Advanced Control
Components)cannot reliably run with 1 kW TWT,
used 300 W TWT instead
Oscilloscope collects 10 acquisitions before moving data into computer memory
Also keeps “average” frame as frame 11
Not efficiently processed: averages frames 1-10 over time as well as frame 11—could delete frames 1-10 after averaging together
Need to use longer valve pulse (~700 µs)
Frame 1 Frame 7
Observations of Previously Assigned Conformers
All simulations from SPCAT, with ab initio dipoles, at 0.9 K.
Noise level ~500 nV (20,000:1 S/N on strongest line)
Observations of Previously Assigned Conformers
Noise level ~500 nV (20,000:1 S/N on strongest line)
Observations of New Conformers
x17.5
Parameter Conformer 2 Theory
A (MHz) 8393.4003(16) 8451.8
B (MHz) 3648.5661(7) 3678.9
C (MHz) 2778.2963(6) 2802.6
ΔJ (kHz) 0.797(15) 0.772
ΔJK (kHz) 4.485(70) 4.88
ΔK (kHz) 3.16(35) 3.44
δJ (kHz) 0.1827(60) 0.177
δK (kHz) 3.14(21) 2.96
Nlines 61
Wt. Std. 0.90
µa (D) 2.496(2) -2.64
µb (D) 0.309(20) 0.28
µc (D) 0.45(8) -0.57
Parameter Conformer 3 Theory
A (MHz) 8572.0553(8) 8643.1
B (MHz) 3640.1063(5) 3672.6
C (MHz) 2790.9666(4) 2818.1
ΔJ (kHz) 0.738(7) 0.719
ΔJK (kHz) 5.276(30) 5.56
ΔK (kHz) 2.53(10) 2.97
δJ (kHz) 0.1631(16) 0.155
δK (kHz) 3.180(31) 3.16
Nlines 57
Wt. Std. 0.88
µa (D) 1.201(3) 1.21
µb (D) 1.916(6) -2.10
µc (D) 0.365(36) 0.45Parameter Conformer 5 Theory
A (MHz) 8536.770(2) 8608.5
B (MHz) 3604.198(1) 3630.1
C (MHz) 2778.331(1) 2802.3
ΔJ (kHz) 0.751(14) 0.714
ΔJK (kHz) 5.29(7) 5.66
ΔK (kHz) 2.75(22) 2.99
δJ (kHz) 0.152(6) 0.143
δK (kHz) 3.34(14) 3.12
Nlines 44
Wt. Std. 1.1
µa / µb 0.28 0.22
µb / µb 1 1
µc / µb 0.88 0.81
Parameter Conformer 6 Theory
A (MHz) 8327.599(5) 8371.4
B (MHz) 3642.001(4) 3674.6
C (MHz) 2776.902(3) 2801.0
ΔJ (kHz) 0.76(12) 0.767
ΔJK (kHz) 5.1(6) 4.81
ΔK (kHz) 2.9(fixed) 2.89
δJ (kHz) 0.24(11) 0.166
δK (kHz) 2.8(fixed) 2.85
Nlines 18
Wt. Std. 1.9
µa / µa 1 1
µb / µa 0.28 0.31
µc / µa 0.49 0.53
Parameter Conformer 1 Theory
A (MHz) 6642.4488(9) 6672.3
B (MHz) 4163.5949(9) 4213.2
C (MHz) 3365.3627(7) 3407.2
ΔJ (kHz) 1.774(29) 1.80
ΔJK (kHz) 6.354(82) 5.55
ΔK (kHz) -4.51(12) -3.28
δJ (kHz) 0.267(13) 0.254
δK (kHz) 1.74(18) 0.89
Nlines 46
Wt. Std. 0.63
µa (D) 2.202(4) 2.35
µb (D) 0 (fixed) -0.03
µc (D) 0.616(10) 0.70
Parameter Conformer 4 Theory
A (MHz) 6634.7621(7) 6654.0
B (MHz) 4160.6347(9) 4217.7
C (MHz) 3377.9063(8) 3424.7
ΔJ (kHz) 1.751(31) 1.74
ΔJK (kHz) 8.21(11) 7.47
ΔK (kHz) -6.51(12) -4.86
δJ (kHz) 0.244(17) 0.244
δK (kHz) 2.72(23) 1.61
Nlines 32
Wt. Std. 0.57
µa / µa 1 1
µb / µa 0.56 0.62
µc / µa 0.56 0.49Parameter Conformer 7 Theory
A (MHz) 6627.612(8) 6659.2
B (MHz) 4146.287(5) 4192.7
C (MHz) 3363.345(6) 3407.8
ΔJ (kHz) 1.84(3) 1.83
ΔJK (kHz) 6.2(2) 5.85
ΔK (kHz) -5.0(3) -3.84
δJ (kHz) 0.23(3) 0.249
δK (kHz) 1.8(3) 1.19
Nlines 20
Wt. Std. 0.50
µa / µc 0.43 0.51
µb / µc 0.30 0.42
µc / µc 1 1
1441 lines present in spectrum at 3:1 S/N or better; 1141 remain unassigned
MW-MW double resonance techniques are necessary to assign these spectra.
blown up 140x from original spectrum
Astronomical Search
New model incorporates grain-surface radical reactions, predicting high abundances of avariety of complex astrochemical species.
CH2OH + CH2OH (CH2OH)2(abundance predicted accurately)
Not incorporated into this model, butpossible similar propanediol formation route existsin this type of chemistry:
CH3CHOH + CH2OH CH2(OH)CH(OH)CH3
(likely more stable) (1,2-propanediol)
CH2CH2OH + CH2OH CH2(OH)CH2CH2(OH)(1,3-propanediol)
Astronomical Search
Since ethylene glycol has been found in Sgr B2(N), both1,2- and 1,3-propanediols were sought in the same source.
For 1,2-propanediol, a total of 12 transitions (six from conformer2, six from conformer 3) were sought. The lowest noise levelattained was ~4 mK. Assuming a temperature of 10 K, the upperlimit on the 1,2-propanediol conformer 3 column density is8 x 1014 cm-2.
For 1,3-propanediol, a total of 22 transitions of conformer 1 weresought; the lowest noise level attained was ~5 mK. The upperlimit on the 1,3-propanediol conformer 1 column density is2 x 1013 cm-2.
For comparison, ethylene glycol column density: 3.3 x 1014 cm-1
Acknowledgements
Funding:National Science Foundation Centers for Chemical Innovation
grant 0847919University of VirginiaJefferson Scholars Foundation (J. Neill)
Tektronix
http://www.virginia.edu/ccu
Conformer 8?
Ab initio (mp2/aug-cc-pvtz):A = 6647.6 MHzB = 4160.1 MHzC = 3369.6 MHzµa = -0.35 Dµb = -2.49 Dµc = 0.35 D
only ~5 transitions might bevisible at current sensitivity