Vibrational spectra of seven halomethanes

Abstract

Seven halogenated methanes CX₂YZ(with X, Y and Z being H, F, Cl, Br or I), all with a plane of symmetry, were synthesized and studied by infrared (IR) and Raman techniques. They belong to point group C_s and have six fundamentals of species a′ and three of species a″. Some of these molecules were investigated 30–40 years ago, but very little spectroscopic work has been carried out since. The IR spectra were recorded in the region from 3100 to 100 cm^–1 in the vapour, liquid and crystalline states. Raman spectra, including semi-quantitative polarization measurements on the liquids, were obtained, additional vapour spectra were recorded, and the liquid spectra were also given in the R(ω) representation. Accurate Raman spectra were recorded of the crystalline phases at temperatures above 78 K, and the external modes in the range 200–10 cm^–1 were investigated as probes for the phase transitions. The fundamentals of chloroiodomethane have been listed and two crystalline phases were observed for this compound, while only one crystal phase was observed for the other molecules. No plastic phases were detected in any of the compounds. Preliminary results of these investigations are presented.