Theoretical study on low-lying states of silicon iodide:MRCI+Q calculation including spin-orbit coupling

Abstract

High-level ab initio calculations are carried out to investigate the fine structure of electronic states correlating with the three lowest dissociation limits of the silicon iodide (SiI) molecule. The potential energy curves (PECs) of 23 Ʌ-S states and 45 Ω states are calculated by using multireference configuration interaction method with the Davidson correction (MRCI+Q). The spin-orbit coupling (SOC) effects are also accounted. Based on the calculated PECs, the spectroscopic constants of the bound states are evaluated, which are in a good agreement with previous experimental results. The predissociation mechanisms of the 22Δ state are studied, the perturbation on vibrational levels and predissociation channels are illuminated. Our investigation indicates that the higher vibrational levels (ν'≥ 7) of the doublet 12Σ+ are perturbed by the crossing quartet sate 14Σ−, which satisfactorily explains the perturbations of the (7,0) and (8,0) rovibronic band systems of the A-X transition detected in previous experiments. In addition, the transition dipole moments (TDMs), Franck-Condon factors (FCFs) and radiative lifetimes for spontaneous emission from the excited states to the ground state are evaluated.