New ab initio potential energy surfaces for the Renner-Teller coupled 1 1 A′ and 1 1A″ states of CH 2

Abstract

New ab initio potential energy surfaces (PESs) for the two lowest-lying singlet 1 1 A′ and 1 1 A″ electronic states of CH 2, coupled by the Renner-Teller (RT) effect and meant for the spectroscopic study, are presented. The surfaces are constructed using a dual-level strategy. The internally contracted multireference configuration interaction calculations with the Davidson correction, using the aug-cc-pVQZ basis set, are employed to obtain 3042 points at the lower level. The core and core-valence correlation effects are taken into account in the ab initio calculations with a modified optimized aug-cc-pCVQZ basis set for the higher-level points. The analytical representations of these PESs, with the inclusion of the nonadiabatic RT terms, are obtained by the nonlinear least-squares fit of the calculated points to three-body expansion. Quantum dynamical calculations are performed on these PESs, and the computed vibronic energy levels for the two singlet electronic states are in excellent agreement with experiment. © 2012 Haitao Ma et al.