Low-Frequency Vibrations of Molecular Solids. X. CH3CCl3, CD3CCl3, CH3CCl2H, and CH3CF3

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Abstract
The far-infrared spectra of solid CH3CCl3 and CD3CCl3 have been investigated from 33 to 400 cm−1. Raman spectra of these solids have also been recorded. The internal torsional mode was observed at 290 and 206 cm−1 in the infrared spectra of solid methylchloroform and methylchloroform-d3, respectively. The threefold periodic barrier to rotation was calculated to be 5.5 kcal/mol. This barrier is compared to those previously reported by other techniques for this molecule and the reported value is much larger than that currently accepted. Four lattice vibrations, 46.9, 53.4, 57.7, and 67.5 cm−1 were observed in the far-infrared spectrum of methylchloroform recorded at − 190°C. Both the effect of temperature variation and deuterium substitution were investigated for these bands. These lattice modes shifted to lower frequency and became quite diffuse as the temperature approached the phase transition at − 68°C. The low-frequency Raman spectrum of methylchloroform at − 165°C showed one line at 38.6 cm−1 which shifted to 37.0 cm−1 with deuteration. The infrared spectra of solid CH3CHCl2 and CH3CF3 have been recorded between 140 and 400 cm−1. The internal torsional mode for 1,1-dichloroethane was observed at 232 and 231 cm−1 for the solid and vapor, respectively. The threefold barrier to rotation was calculated to be 3.50 kcal/mol. The internal torsion for methylfluoroform was observed at 220 cm−1 for the solid, and the barrier was calculated to be 3.29 kcal/mol. Substituent effects on the barrier heights are discussed.

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