Ab initio and empirical approaches to the general harmonic force field of methylene chloride

Abstract

An ab initio gradient calculation of the general harmonic force field (GHFF) of methylene chloride at the HF-SCF/6-31 G** level has been undertaken. The results compare favourably with those determined empirically, thus demonstrating a good predictive capability at this level of sophistication for a molecule possessing two third row halogen atoms. The ab initio results reveal small inadequacies in the empirical force constants relating to the CH₂ moiety, which may be corrected by a careful re-appraisal of the accumulated spectroscopic data. The resulting empirical and scaled quantum mechanical (SQM) sets of force constants are then in very good accord. Predicted ab initio cubic force constants for methylene chloride are also calculated.