Theoretical and Experimental Spectroscopy of the S2 State of CHF and CDF: Dynamically Weighted Multireference Configuration Interaction Calculations for High-Lying Electronic States

Dynamically adjusting the weights in state-averaged multiconfigurational self-consistent field (SA-MCSCF) calculations using an energy dependent functional allows the electronic wave function to smoothly evolve across the potential energy surface (PES) and correctly preserves differing asymptotic electronic-state degeneracy patterns. We have developed a generalized dynamic weighting (GDW) method to treat high-lying electronic states. To test the method, a global PES was constructed for the S-2((B) over tilde) state of CHG(CDF) which lies nearly 31000 cm(-1) above the minimum of the ground state. The GDW method was used to produced SA-MCSCF references states for subsequent multireference configuration interaction (MRCI) calculations, whose Davidson-corrected energies were extrapolated to the complete basis set limit. Quantum mechanical vibrational energy calculations for CDF were performed using the fitted PES, and the predicted energy levels are in excellent agreement with an extensive set of experimentally determined (optical-optical double resonance) levels, with a mean unsigned error of only 12 cm(-1).