Absorption Spectrum of Rubidium in the Presence of Isomeric HydrocarbonsOleg Jefimenko and Joel Anderson Gwinn Citation: The Journal of Chemical Physics 29, 148 (1958); doi: 10.1063/1.1744413 View online: http://dx.doi.org/10.1063/1.1744413 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/29/1?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Electronically excited rubidium atom in helium clusters and films. II. Second excited state and absorptionspectrum J. Chem. Phys. 134, 024316 (2011); 10.1063/1.3528936 Interferometric measurement of the resonant absorption and refractive index in rubidium gas Am. J. Phys. 74, 1055 (2006); 10.1119/1.2335476 The role of hyperfine pumping in multilevel systems exhibiting saturated absorption Am. J. Phys. 72, 631 (2004); 10.1119/1.1652039 Optimization of resonant two-photon absorption with adaptive quantum control Appl. Phys. Lett. 80, 4265 (2002); 10.1063/1.1481188 Absorption Spectrum of Cs in the Presence of Isomeric Hydrocarbons J. Chem. Phys. 39, 229 (1963); 10.1063/1.1734007

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THE JOURNAL OF CHEMICAL PHYSICS VOLUME 29, NUMBER 1 JULY, 1958

Absorption Spectrum of Rubidium in the Presence of Isomeric Hydrocarbons

OLEG JEFIMENKO AND JOEL ANDERSON GWINN

Department oj Physics, West Virginia University, Morgantown, West Virginia

(Received January 2, 1958)

Absorption spectra of Rb in the presence of various hydrocarbons (ethylene, propylene, butene-I, iso­butylene, isobutane, n-pe~tane, isopentane, neopentane, n-hexane, 3-methylpentane, 2, 3-dimethylbutane, and neohexane) were studIed for the purpose of determining the dependence of the collision-induced satellite bands on the structure of colliding particles. It was found that the positions of the low-temperature red bands are regularly affected by the differences in structure of the hydrocarbon molecules. In particular, the least branched (straight chain) isomeric molecules produce bands with the smallest band-line separations, and the most branched molecules with four or three methyl groups attached to the same carbon atom pro­dnce bands with the largest band-line separations. On the other hand, the positions of the high-temperature red bands as well as the positions of the violet bands are not noticeably affected by the differences in molecu­lar structure of the hydrocarbon isomers employed in this work.

INTRODUCTION

THE results of recent investigations of the spectra of binary gaseous mixturesl-6 indicate that the ap­

pearance of the collision-induced bands in the neighbor­hood of the atomic lines is a much more common phenomenon than previously believed. In fact, it seems that quite generally the spectra of gaseous mixtures constitute what may be called "interaction spectra" exhibiting bands and diffuse lines which are not present in the spectra of the components of these mixtures taken separately. A study of the collision­induced bands is therefore of a considerable interest both because of the theoretical implications of the existence of these bands and the significance of their presence for spectrochemical analysis.

The present work was undertaken to investigate the absorption spectrum of Rb in the mixtures of Rb with various hydrocarbon isomers in order to determine the dependence of Rb-hydrocarbon bands on the structure of hydrocarbon molecules. Both saturated and un­saturated hydrocarbons were used. The saturated hydrocarbons were isomers of butane, pentane, and hexane. The unsaturated hydrocarbons were butene-l and its isomer isobutylene and also ethylene and propylene.

EXPERIMENTAL

The absorption tube was of the cold-window type, similar to that used previously.1-3 The hydrocarbon pressure in the tube ranged from 0.3 to 1 atmos. The spectra were photographed with a JAco Wadsworth stigmatic 1.5 m wide angle spectrograph, with a 15 000 grooves/in. grating and a dispersion of 10.9 and 5.45

1 Ch'en, Bennett, and Jefimenko, J. Opt. Soc. Am. 46, 182 (1956).

2 S. Y. Ch'en and O. Jefimenko, J. Chern. Phys. 26, 256 (1957). 3 O. Jefimenko and S. Y. Ch'en, J. Chern. Phys. 26, 913 (1957). 4 O. Jefimenko and W. Curtis, J. Chern. Phys. 27, 953 (1957). 5 S. Robin and St. Robin, J. phys. radium 18, 411 (1957). 6 S. Y. Ch'en and T. H. Warnock, Bull. Am. Phys. Soc. Ser.

II,2, 372 (1957).

A/mm in the first and second order, respectively. The slit was 40 J.i. wide. Kodak I-N film was used for photo­graphing the resonance lines, and Kodak 103-0 film was used for the higher members.

RESULTS AND DISCUSSIO N

The spectra of all Rb-hydrocarbon mixtures investi­gated in this work exhibit narrow diffuse bands on the long wavelength side of the Rb atomic lines (low-tem­perature red bands3) belonging to the first three or four principal series doublets. The position data of these bands are given in Table I, where the notations are the same as in the tables of the references 1-4.

The analysis of the position data may be summarized as follows:

1. Within each isomer the band-line separations (.6.vm ) are larger for the bands produced by the isomers whose molecules possess more branching, and the largest separations correspond to the isomers whose molecules have four or three methyl groups attached to the same carbon atom (Fig. 1). It appears, therefore, that the larger band-line separations are produced by isomers whose molecules are more compact, which may mean that the dispersion forces are larger for such molecules.

FIG. 1. The low-temperature red bands near Rb lines of the secon~ principal series doublet in the spectra of the mixtures of Rb WIth n-pentane (upper spectrum), with isopentane (middle spectrum), and with neopentane (lower spectrum).

148

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ABSORPTION SPECTRUM OF RUBIDIUM

TABLE I. Low-temperature Rb-hydrocarbon red bands."

Hydrocarbon Band near longer wavelength

component ('P" ,)

Maximum 6.v", Structural formula and name Mass formula cm-1 cm-1

I. For the Rb resonance lines

CH,:CH, (ethylene) C,IL * 12555. 7±8 -23.2 CH,: CHCH. (propylene) C.H6 552.1±6 -26.8

CH.CH,CH: CH, (butene-1) C,H8 546.2±3 -32.7 CH.CH:CHCH. (butene-2) C,H8 549.3±2 -29.6 CH,: C(CH.)CH. (isobutylene) C,H8 548.2±3 -30.7

CH.(CH,),CH. (n-pentane) C,H12 544.4±4 -34.5 (CH.), CHCH,CH. (isopentane) C,H'2 542.9±4 -36.0 (CH.),C (neopentane) C,H" 542.2±4 -36.7

CH.(CH,),CH. (n-hexane) CsH" w 536.2±3 -42.7 CH.CH,CH(CH.)CH2CH. (3-methylpentane) C6H

" 541.3±5 -37.6

(CH.),CHCH(CH.), (2, 3-dimethylbutane) C6H" 538.7±5 -40.2 (CH.).CCH2CH. (neohexane) C6H" 537.6±5 -41.3

II. For the Rb second absorption doublet

CH,:CH, (ethylene) C,H, Red asymmetry CH,:CHCH. (propylene) C.H, 23691.3±5 -23.7

CH.CH,CH:CH, (butene-1) C,Ha 690.3±3 -24.7 CH.CH:CHCH. (butene-2) C,Hs 688.5±1.5 -26.5 CH,: C(CH.)CH. (isobutylene) C,Ha 683.5±3 -31.5

CH.(CH,),CH. (n-butane) C,HIO 686.2±1.5 -28.8 (CH.).CH (isobutane) CoHIO 681.0±2 -34.0

CH.(CH,).CH. (n-pentane) C,H12 680.0±1.5 -35.0 (CH.),CHCH,CH. (isopentane) CoH" 678.4±1.5 -36.6 (CH.),C (neopentane) C,H12 670.0±1.5 -45.0

CH.(CH,),CH3 (n-hexane) C,H" 673.3±1.5 -41.7 CH.CH,CH(CH.)CH,CH3 (3-methylpentane) C,H" 671.2±1.5 -43.8 (CH.),CHCH(CH3), (2, 3-dimethylbutane) C,H" 670.7±1.5 -44.3 (CH3)'CCH,CH. (neohexane) C,H" 669.8±1.5 -45.2

III. For the Rb third absorption doublet

CH,:CHCH. (propylene) C.H, * 27822.8±2 -12.1

CH.CH:CHCH. (butene-2) C,Ha 823±3 -12 CH,: C(CH.)CH. (isobutylene) C,Ha w 806.2±4 -28.7

CH.(CH,).CH. (n-pentane) COH12 822.1±1 -12.8 (CH.),CHCH,CH. (isopentane) C,H" 820.0±1 -14.9 (CH.),C (neopentane) CoH" 798.2±2 -36.7

CH.(CH,),CH. (n-hexane) C,H" 819.7±1 -15.2 CH.CH,CH(CH.)CH,CH. (3-methylpentane) C,H" 819.0±1 -15.9 (CH.),CHCH(CH.), (2, 3-dimethylbutane) C6H" 813.7±1 -21.2 CH.).CCH,CH. (neohexane) C6H" 808.0±1 -26.9

IV. For the Rb fourth absorption doublet

CHa(CH,).CH. (n-pentane) COH12 * 29827.5±2 -6.8 (CH.),CHCH,CH. (isopentane) CoH" * 823.6±2 -10.7

CH.(CH,),CH. (n-hexane) C6H" * 828.0±1 -6.3 CH.CH,CH(CH.)CH,CH. (3-methylpentane) C6H" * 828.0±1 -6.3 (CH.)'CHCH(CH.), (2, 3-dimethylbutane) C6H" 823.0±1 -11.3 (CH.).CCH,CH. (neohexane) C6H" 819.6±1 -14.7

a These bands are observable when the temperature of the absorption tube is 200-300'C. b Position data are taken from reference 2.

149

Band near shorter wavelength component ('P",)

Maximum 6.vm cm-1 em-I

* 12796.1±1O -20.4 * 782.3±8 -34.2

w 775.2±4 -41.3 773.0±3 -43.5b 770.0±3 -46.5

w 773.0±4 -43.5 770.4±4 -46.1 769.2±4 -47.3

w 766.4±4 -50.1b w 771.0±7 -45.5

768.4±7 -48.1 764.5±5 -52.0

Red asymmetry * 23767.3±1O -25.2

w 762.6±4 -29.9 763±3 -29.5b 759.4±3 -33.1

762.3±2 -30.2b 759.0±2 -33.5

758.1±2 -34.4 756.7±2 -35.8 748.7±2 -43.8

754.5±2 -38.0 751.4±2 -41.1 748.6±2 -43.9 747.4±2 -45.1

* 27858.6±2 -11.3

858±3 -12b w 845.4±4 -24.5

w 855.0±2 -14.9 852.6±1 -17.3

w 847.4±2 -22.5

853.2±1 -16.7 851.5±1 -18.4 850.1±1 -19.8 847.2±1 -22.7

* 29844.2±3 -9.4 * 842.0±2 -11.6

* 845.0±1 -8.6 * 845.0±1 -8.6 * 843.4±1 -10.2

842.1±1 -11.5

2. The effect of differences in molecular structure on the positions of the bands is more pronounced for lighter isomers than for heavier ones. For instance, the ~Vm variations associated with structural differ­ences in the pentanes are larger than the ~Vm variations associated with similar structural differences in the

hexanes. This seems to reflect a more gradual change in the "compactness" of the heavier isomeric molecules that takes place with a change in branching, as com­pared with the corresponding change of the "com­pactness" of the lighter isomeric molecules.

3. The bands associated with the Rb resonance lines

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150 O. JEFIMENKO AND J. A. GWINN

I H

,))\l..... L Rb L Rb

(al

""";,J '''I..:....... H L RbLRb (b)

FIG. 2. The high-temperature and the low-temperature red bands in the spectrum of Rb-neohexane mixture for the third (al and the fourth (b) Rb principal series doublet. The high-temperature bands are designated by "H," the low·temperature bands are designated by "L," and the lines of Rb are designated by "Rb." At the fourth doublet (b) the high-temperature band and one low-temperature band may be observed simultaneously.

TABLE II. High-temperature Rb-hydrocarbon red bands.'

Hydrocarbon

Structural formula and name Mass formula Maximum

cm-1

I. For the Rb third absorption doublet

CH,),C (neopentane) C,Hlz 27737.6±4

CH 3(CH2),CH3 (n-hexane) C,HB 723.9±8 (CH3)2CHCH(CH3), (2,3- C.H14 721.6±8

dimethylbutane) (CH,lsCCH,CHs (neo- CfiHl4 716.9±8

hexane)

II. For the Rb fourth absorption doublet

CH 3(CH')4CH, (n-hexane) C,HI4 29796.0±4 CH,CH2CH (CHs)CH,CH3 Corb 796.0±4

(3-methylpentane) (CH,),CHCH(CH 3), (2,3- C,H14 797.7±4

dimethylbutane) (CH3)3CH2CH3 (neo- C,H14 799.S±4

hexane)

-97.3

-111.0 -113.3

-118.0

-38.3 -38.3

-36.6

-34.8

• These bands are observable when the t.emperature of the absorption tube is 350°-400°C. All separations are measured from the long wavelength component of the doublets.

are the least sensitive to the differences in the molecular structure of the hydrocarbon isomers. This sensitivity increases with increasing order of the doublets.

The shape of the low-temperature red bands at the resonance lines is also influenced by structural differ­ences of the interacting particles. The bands produced by isomers whose molecules are more compact are narrower and better defined than the bands produced

by isomers whose molecules are less compact. However, the shape of the bands at the lines of the second and higher order doublets does not appear to be definitely influenced by these differences in structure.

It was found that at temperatures about 70ce higher than those required to produce the above described red bands, a second red band (high-temperature red band3) could be seen on the long wavelength side of the third and fourth Rb principal series doublet (Fig. 2). Bands of this type were observed for neo­pentane and isomers of hexane. The secondary bands have the same appearance as the red bands already described but are considerably farther from the atomic lines and much wider. Such bands were not found near the resonance lines, but traces of them were observed at the second doublet. The position data of these bands are given in Table II. As may be seen from this table, these bands do not appear to be appreciably affected by the structural differences in the hydrocarbon molecules of the same isomer.

The bands on the short wavelength side (violet bands) were also observed. An analysis of the positions of these hands does not, however, indicate that they are definitely affected by differences in the structure of isomeric hydrocarbons.

ACKNOWLEDGMENT

The authors wish to thank David W. Stemple for his assistance in the latter part of this research.

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