MRCI+Q calculations on electronic structure and spectroscopy of low-lying electronic states of silicon monobromide including spin-orbit coupling effect

The electronic structures of silicon monobromide (SiBr) correlating with the lowest three dissociation channels are studied using high-level configuration interaction method. The spin-orbit coupling (SOC) effect and core-valence (CV) correlations effect are taken into account to improve the accuracy of electronic structures. Based on the calculated electronic structures of the lowest three dissociation channels of SiBr, the spectroscopic constants of quasibound and bound electronic states are fitted, which are coincided with the results of experiment. The dipole moment curves (DMs) of the lowest three dissociation channels of SiBr are obtained, and the abrupt change of DMs nearby the avoided crossing point are explained by the variation of electronic configurations of the corresponding states. With the help of the calculated SOC matrix elements, the predissociation channels of the low-lying vibrational states of ²Δ(Ⅱ) and ²Π(Ⅲ) sates are analyzed. The complicated interaction between crossing states is investigated. The ν'≥0 vibrational states of ²Δ(Ⅱ) and ν′≥2 vibrational states of ²Π(Ⅲ) would predissociate rapidly through predissociation channels of ²Δ(Ⅱ)-²Π(Ⅱ) and ²Π(Ⅲ)-²Σ⁺(Ⅱ). Finally, the transition properties of A²Σ⁺-X²Π, ²∆(Ⅱ)-X²Π, ²Σ⁺(Ⅱ)-X²Π, ²Π(Ⅲ)-X²Π, 1/2(Ⅱ)-X²Π_1/2, 1/2(Ⅲ)-X²Π_1/2 and 3/2(Ⅱ)-X²Π_1/2 transitions are investigated, and radiative lifetime of bound states are evaluated.