An iterative perturbation theory-based algorithm for calculation of diagonal force constants of the nu(3) modes in quasi-tetrahedral systems with lowanharmonicity

A novel, stationary perturbation theory - based iterative algorithm for cal culation of the diagonal force constants of the vs modes in tetrahedral and quasi-tetrahedral systems with low anharmonicity is developed. The diagona l elements in the potential energy expression are calculated on the basis o f experimentally measured fundamental and second-order transition wavenumbe rs, in a self-consistent manner. Perturbation corrections up to the second order are included in the model. The procedure is rapidly convergent, simpl e, and may be easily implemented within computer programs. The calculated d iagonal force constants are consistent with the measured fundamental and se cond-order transition wavenumbers. The proposed model is applied to several isomorphously isolated (distorted-tetrahedral) sulfate impurities in selen ate and chromate matrices. Experimental data for these systems were obtaine d by FT-IR spectroscopy.