THE FORCE-FIELD OF BROMOFORM - A THEORETICAL AND EXPERIMENTAL INVESTIGATION

The potential function of bromoform has been determined in a joint eff ort, comprising ab initio and genetic algorithm calculations and a ref inement to observed and anharmonicity corrected wavenumbers. To this e nd, the infrared and Raman spectra of HCBr3, DCBr3, and (HCBr3)-C-13 h ave been recorded in the gas and liquid phases, those of the last spec ies for the first time, In the analysis of the spectra, a number of co mbination and overtone bands have been assigned, besides the fundament al vibrations, leading to the determination of some anharmonicity cons tants. This is also the first experimental determination of such const ants for the deuterated and C-13 molecules, A Fermi interaction in the spectrum of DCBr3 affecting v(4) and v(3) + v(5) has been interpreted , and the corresponding cubic potential constant has been evaluated. T he value of some of the force constants determined in the ab initio an d genetic algorithm calculations has been of key importance to allow c onvergence in the refinement process. The experimental frequencies are well reproduced by the force fields.