U . S. Department of Commerce Research Paper RP1814 National Bureau of Standards Volume 391 July 1947 Part of the Journal of Research of the National Bureau of Standards Infrared Absorption Spectrum of Carbon Disulfide By Earle K. Plyler and Curtis 1. Humphreys The infrared absorption spectrum of carbon disulfide has been remeasured in the region from 2 to 24 I' with cells up to 5 mm in t hickness. Fifteen bands were observed, some how­ ever being of low intensity. The strongest band for the liquid occurs at 6.621', and t he second harmonic of this band was observed at 2.22 1', but t he first harmonic, which should be at about 3.33 1', was not observed, in accordance with the selection rules for a symmetrical linear molecule. Four combination bands were observed between 3 and 5 1' , whose wave­ lengths " 'ere in good agreement with the calculated values. A combination band, which is represented by the difference between t wo fundamentals, occurs as a broad, moderately st.rong band in t he region of 11.61'. A weak band, observed at 15.271-'< corresponds with the wavelength of the inactive vibration of the molecule. However, when t his region was tudied with a 140 cm cell filled with the saturated vapor of C82 at room temperature, no baml was observed. In the vapor state a total of six bands were found at wavele,1gths less than 201'. The fundamental band at 6.5 I' shows a side branch that is probably due to t he isotopic effect produced by C13. 80me small bands t hat were observed may be attribu ted to the 02832834 molecule. As would be expected for this molecular configuration, the spectrum of C82 as observed may be classified into an array of terms analogous to those of CO2• A band at 12.7 I' has different intensities for samples obtained from two differen t sources and may be caused by an impurity. This band did not appear when the cell containing the vapor was used. I. Introduction absorption spectrum of compounds. Carbon tetra­ chloride, another commonly used substance, is The infl'alled 'absorption spectrum of carbon disulfide has been measured by many observers quite absorbing from 12 to 15 p" and is not as satisfactory as CS2 for use as a solvent when ab­ I [1, 2, 3].1 The present work has been undertaken primarily to extend the observations to the short­ sorption measurements are made in this part of the spectrum. I wavelength region , also to compare the spectrum of the liquid with the vapor. In the ncar-infrared The absorption spectrum of the vapor of CS2 has been measured by Bailey and Cassie [2] and I region CS2 is qu~te transparent, and cell t.hicknesses of several centlmeters may be used WIth only a by Dennison and Wright [3], and the molecular small loss in energy. However, because of the structure has been determincd to be of the type of CO2. That is, the molecule is linear, and the presence of strong bands at 4.6 and 6.5 p" and carbon atom is at the center. Further work by other bands at 3.4 and 3.55 p" very thick cells are almost opaque beyond 3.3 p,. 1ifany substances Sanderson [4] on th e finc structure of the 4.6 p, band have strong [L bsorption bands in thE' region between has revealed that the rotational lines are equally 7 and 15 p,. For this region, layers 0.1 mm in spaced, which is further proof that the molecul e thickness arc quite transparent, and carbon disul­ is linear. Also, Lieberman [5] has resolved a band fide may be used as a solvent in the study of the in the ultraviolet and found that the rotational lines wcre equally spaced. The Raman spectrum I Figures in brac kets indicate the literature rererences at the end or this paper. of CS2 has been measured by a number of observers, Absorption Spectrum of Carbon Disulfide 59 and such data are of great assistance in interpreting of the spectrum. In figure 1 the results for cells the energy levels. 5.0 mm and 0.10 mm in thickness have been The selection rules for the energy-level transi­ plotted on the same graph. The 5.0-mm cell tions in a linear symmetrical molecule are well showed all the bands that were observed, but in. known. :Many of the energy transitions are inac­ the region of 6.6 and 4.6/J-, the bottoms of the tive. In this work on th e absorption of the mate­ bands were broad, and the positions of maximum rial in the liquid state, a number of banels are absorption could not be accurately determined. found that have not been observed for the gaseous In table 1 the wavelengths of all the observed state. This will be discussed after the experi­ bands are given. The values of the observed mental results are given. wavelengths are obtained by taking the average of a number of observations. II. Experimental Results Different cell thicknesses ·were used to display A Perkin-Elmer infrared spectrometer was used the different bands t.o best advantage; for example, to measure the absorption spectrum of carbo]] the band at 2.22 /J- absorbs about 15 percent of the disulfide. In addition to the rock-salt prism, a radiation with a cell thickness of 5.0 mm, whereas LiF prism was used in the region from 3.3 to 3.7/J­ the 4.6- and 6.6-/J- bands absorb 100 percent for a and a KBr prism from 15 to 24/J-. A slit-control cell 0.10 mm in thickness. The 3.55-/J- band device, which has been described before [6], was showed a slight side band on the long-wavelength found to simplify the measurements, especially in side. When this region was investigated with a the long-wavelenzth region. The experimental LiF prism, figure 2, the two bands were resolved 9,rrangements were the same as formerly used, and separated by about 23 cm- I . The band at and the description will not be repeated here. 6.62 /J- is very intense and showed zero transmission Severa 1 cell thicknesses were used in various regions from 6.50 to 6.70 J.L with a 0.05-mm cell. The WAVE NUM BER S IN CM-' pOOO 4000 3000 2500 I 20,°0 1500 14,00 1300 1200 1100 ,I I , I , , , 100 V r= ---- \\0 /" ~ ~ 80 1\ !r\ / ~'" r----..- V '\ 60 \ \ I ! \ II 40 . \ 20 \ I ) ) a J \ \ 2 .0 2.5 3.0 3 .5 4 .0 4 .5 5.0 5.5 6.0 6 .5 7 .0 7 . 5 8.0 8.5 9 .0 9.5 WAVELENGTH IN MICRONS WAVE NUMBERS I N CM_I 1100 1000 eoo 990 , , , , , 79 0 , 100 - - ~ ~ ~ '-.",. /' - - eo '\ '" 60 LI \ ~ /"\. ( 40 \ ( ~ "-J '-...... 20 \ "" ~ \ ) 9. 5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14 .0 14.5 15.0 WAVELENGTH I N M IC RON S FIGURE I.- I nfrared transmission of liquid CS 2 for cells of 5 mm and 0.1 mm in thickness. 60 Journal of Research bands, as observed with a rock-salt prism are 10 0 fairly sharp and are probably not over 0.02 )J. in error. The bands at 11.68 and 12.77 )J. are broad, I( and it is somewhat difficult to determine acc urately 80 \ their maxima of absorption. In the region of 14 )J. z 0 there is an indication of a band wh en a 5.0-mm <J) cell is used, but with thinner cells no band was <J) ~ 60 \ <J) \ I observed. F or the thick cells there is considerable z r ct ~I general absorption in this region. This is partly II:.... I due to a band at 15.27 )J.. This was the only band .... observed beyond 15 )J. There is a small dip at z 40 J llJ \ U 20 )J. , but this was not sufficien t to be considered 0:: llJ VV as a band, especially as it occurs in a region of lL general absorption and may be due to experimen tal 20 error. The percen tage transmission is decreasing as the long-wavelength region is reached, and this is caused by the 25 -JL band. o~ ____~~ __~~ ____~ ____~ 3 . 3 3.4 3 .5 3.6 3 .7 T ABLE I. - Observed and calculated bands of carbon dl:su lfide WAVELENGTH IN MICRONS 'Vave number F IG URE 2.-Spectrum of liquid CS2 in the re gion of 3.6 J1. as 'Vav~­ 'r erm leogt h measllred with a LiF prism (fell thickness about 1.2 111m). Observed Calculated observed --------------------1-------1------------ 100 cm-i cm- i Vl____ ___________________________ ____ _ 655 I' z 1655 15. 27 0 ----.. 112 _______________________________________________ _ r---.... 1397 ----.-.----- iii 80 V3 _ _________ • ________________________ _ "! /--- ~ 1,510 11,510 6.64 ;!; V 111+ 2 _______________________________ _ (J) 11 1, 048 1, 052 9.54 z 60 I / ~ « 2v, _______ ____________________________ { 807 794 12.39 a: f- ~ 783 --.--------- 12. 77 40 I / ~ - f- V" V'-Vl __________ _____ ________________ · { 855 855 11. 66 z II w "" 1, 197 1, 191 8. 35 0 i'- 3112 _________ _ _ _ __ _ ___________________ _ a: 20 I~ r---- 1, 180 ------------ 8. 47 w VZ+vl ___________________ _____________ _ 1,910 1, 907 5. 23 Q.