The farhyphen;infrared spectrum of gaseous CD3CD3has been measured in the region of the torsional fundamental under relatively large pressurehyphen;path length conditions. The observations were made using a modified Bomem spectrometer at a resolution of 0.016 cmminus;1, an absorption path of 20 m, and a gas temperature and pressure of 168 K and 80 Torr, respectively. The prominent features of the spectrum are theP,Q, andRbranches of the torsional fundamental (v4=1larr;0) and theQbranch of the first torsional overtone (v4=2larr;1). ThePandRbranches of the fundamental consist of peaks about 0.2 cmminus;1wide due to unresolved structure. In addition, a very high resolution (0.0014 cmminus;1) spectrum of the lowest lying degenerate fundamental ngr;9of CD3CD3was obtained. From the combined intensity and frequency analyses of the farhyphen;infrared spectrum and 442 lower state combination differences in ngr;9and its associated hot band ngr;9+ngr;4minus;ngr;4, the effective leading coefficientsVtilde;3=989.10(68) cmminus;1andVtilde;6=9.47(29) cmminus;1in the Fourier expansion of the hindering potential were determined. The rotational constantBwas found to be 13thinsp;802.658(39) MHz and four distortion parameters were obtained. The torsional dipole constants mgr;perp;and mgr;par;minus;mgr;perp;were determined to be 7.41(74) and minus;19.9(2.0) mgr;D, respectively. The experimental values of mgr;perp;and mgr;par;minus;mgr;perp;are shown to be in good agreement with values calculated from theoretical expressions. The shape of the torsional bands can be reproduced in detail with the model adopted here.
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