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

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 X2Π and A2Σ+ states, respectively. For the linear HSAl+ structure, the first excited state is A2Σ+. The X2Π 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 12A′ and 12A″ PESs, respectively. The CASPT2/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. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011