Ab initio study of the low-lying electronic states of the [formula omitted] anion

Abstract

Six low-lying states (X2Σg+, A2Πu, B2Σu+, 4Σg+, 4Πu and 4Σu+) of C2− anion are studied by highly correlated ab initio calculations. The potential energy curves (PECs) are computed in the internuclear separation from 0.8 to 5.0Å using the complete active space self-consistent field method, and then performing the internally contracted multireference configuration interaction with Davidson correction. Core–valence correlation and scalar relativistic effect are considered through employing the aug-cc-pcV5Z-dk basis set. The spin–orbit coupling of the A2Πu state is also calculated using Breit–Pauli Hamiltonian. Based on the PECs derived from the high-level ab initio calculations, the spectroscopic parameters are obtained by fitting the ro-vibrational levels that are acquired by solving the ro-vibrational Schrödinger equation. These spectroscopic parameters, especially for low-lying doublet states, are in good agreement with the previously calculated and experimental results. Finally, the electronic transition dipole moment matrix elements, Franck–Condon factors, radiative lifetimes and oscillator strengths of A2Πu–X2Σg+andB2Σu+-X2Σg+ are calculated and discussed as well.