An ab initio study of the structures and vibrational spectra of chromium oxo-anions and oxyhalides

The bond distance and vibrational spectrum of the chromate(VI) ion has been calculated using HF-SCF and SCF-density functional (SCF-DFT) methods in conjunction with a wide range of basis sets. It was found that the B3-LYP/LanL2DZ combination gave the best fit for the observed vibrational spectrum. The molecular geometries and vibrational spectra of chromate(V), dichromate, trichromate, chlorochromate, fluorochromate, chromyl chloride, and chromyl fluoride were also calculated using B3-LYP/LanL2DZ. Force constants and potential energy distributions were determined from the calculated spectra, after appropriate scaling, which compare favorably with the experimental IR and Raman spectra. Precise vibrational band assignments have been determined for dichromate and trichromate. Relationships have been established between the CrO bond distance and CrO principal stretching force constant.