Ab initio anharmonic force field, spectroscopic parameters and equilibriumstructure of trifluorosilane

The quadratic, cubic and semidiagonal quartic force held of trifluorosilane has been calculated at the MP2 level of theory employing a basis set of po larized valence triple-zeta quality. This force field has been used to pred ict the spectroscopic constants, including the parameters specific of the d ouble degenerate vibrational states. The calculated values are found to be in good agreement with the available experimental data, and explanations ar e offered for discrepancies. This confirms the accuracy of the ab initio fo rce field and the validity of the theory of the reduction of the rovibratio nal Hamiltonian of a doubly degenerate vibrational state. The equilibrium s tructure has been derived from the experimental rotational constants and th e ab initio rovibrational interaction parameters. This semiexperimental str ucture is in excellent agreement with the ab initio equilibrium geometry.