Force Constants for Some Halomethanes

Abstract

Valence‐type force constants, including several interaction terms, have been deduced from some of the experimentally observed fundamental vibration frequencies of the molecular sequence CX₄, CX₃Y, CX₂Y₂, CXY₃, and CY₄ in which X may be chlorine or bromine, Y hydrogen or deuterium. By assuming that the force constants are invariant for the different molecules and by neglecting several interaction constants associated with two bending motions, the number of distinct constants was reduced to 28, from which, after slight adjustment, 100 vibration frequencies were calculated. The quality of the fit with the experimental frequencies is indicated by a reasonably low root mean square deviation between calculation and observation (1.1 percent for 82 frequencies) and by the success of the constants in predicting 22 of the frequencies which were not used in the initial numerical evaluation of the constants.