Ab initio investigation on predissociation of the A2Σ+ state of the SeH radical induced by spin-orbit coupling

Abstract

High-level ab initio calculations are performed to investigate potential energy curves (PECs) of seven low-lying Λ-S states associated with the two lowest dissociation limits of the SeH radical by utilizing the internally contracted multireference configuration interaction (icMRCI) method in combination with the aug-cc-pwCV5Z Gaussian basis set. The scalar relativistic effect (SR), the electronic core-valence (CV) correction, and Davidson (+Q) modification are included in our calculations. The fourteen Ω states generated from the seven Λ-S states are yielded when the spin-orbit coupling (SOC) effect is taken into account by using the Breit-Pauli operator. On the ground of the obtained PECs, the spectroscopic constants of the bound Λ-S and Ω states are evaluated, which reproduce pretty well the available experimental and theoretical values. By virtue of SOC matrix elements between the bound A2Σ+ state and repulsive 4Σ–(I), 2Σ–(I), or 4∏(I) states crossing with the A2Σ+ state PEC, the spin-orbit perturbations in the A2Σ+ rovibrational manifold in the crossing region and the A-state predissociation mechanism are analyzed. It is clearly exhibited that the avoided crossing phenomena between electronic states possessing the same Ω quantum number provide obvious spectroscopic effects in the transition dipole moments (TMDs) and Franck-Condon factors (FCFs) of the A2Σ+-X2Π transition. The radiative lifetimes of the A2Σ+ vibrational sublevels are determined. In addition, we finalized our study of the SeH molecule by optimizing its equilibrium ground state geometry in terms of a restricted coupled cluster approach including singles and doubles with perturbative triples account (RCCSD(T) method) plus CV, SR, and SOC corrections with extrapolating to complete basis set (CBS) limit.