Theoretical prediction on HAlS ~+ and HSAl ~+ cations using multiconfiguration second-order perturbation theory

摘要

Some low-lying states of the HAlS ~+ and HSAl ~+ cations have been studied for the first time by large-scale theoretical calculations using three methods: complete active space self-consistent field (CASSCF), complete active second-order perturbation theory (CASPT2), and density functional theory Becke's three-parameter hybrid function with the nonlocal correlation of Lee-Yang-Parr (B3LYP) with the contracted atomic natural orbital (ANO-L) and cc-pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces (PESs) were optimized at the CASSCF/ANO-L and B3LYP/cc-pVTZ levels. The ground and the first excited states of linear HAlS ~+ are predicted to be X ~2Π and A ~2Σ ~+ states, respectively. For the linear HSAl ~+ structure, the first excited state is A ~2Σ ~+. The X ~2Π state of linear HSAl ~+ is a second-order saddle point, because it has two imaginary frequencies. Two bent global minima M1 and M2 were found along the 1 ~2A' and 1 ~2A″ PESs, respectively. The CASPT~2/ANO-L potential energy curves of isomerization reactions were calculated as a function of HAlS bond angle. According to our calculations, the ground-state HAlS ~+ is linear, whereas the ground-state HSAl ~+ is bent.