Motions of Molecules in Condensed Systems. VI. The Infra-Red Spectra for Vapor, Liquid, and Two Solid Phases of Methyl Chloroform

Infra-red spectra are compared for equivalent absorbing paths of methyl chloroform (1,1,1-trichloroethane) as vapor at 25°, liquid at −28°, solid I at −40° and solid II at −55°C. The spectra differ in the respects: (1) P-Q-R branches observed on some bands in the vapor disappear in the condensed phases, (2) bands generally are sharpened and ones attributable to combinations are intensified by condensation, and (3) three weak bands at 830, 1288, and 1313 cm−1 are present in the condensed states only. Although selection rules for the vapor exclude only the torsional mode and its combinations with other, totally symmetric ones, these weak bands would yield what appears to be the unreasonably high value of 300 cm−1 for the torsional frequency. The fundamental frequencies are discussed briefly and it is pointed out that the spectra are almost entirely explicable upon the basis of only ten of the twelve expected ones for this molecule.