Theoretical study on low‐lying states of HAlO+ and HOAl+ cations

Some low‐lying states of HAlO⁺ and HOAl⁺ cations have been studied using the complete‐active‐space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) methods with the contracted atomic natural orbital (ANO) basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO and CASPT2/ANO levels. The ground and the first excited states of HAlO⁺ are predicted to be X²Π and A²Σ⁺ states, respectively. It was predicted that the ground state of HOAl⁺ is X²Σ⁺ state. The A²Π state of HOAl⁺ has unique imaginary frequency. A bent local minimum M1 was found along the 1²A″ potential energy surface, and the A²Π state of HOAl⁺ should be the transition state of the isomerization reactions for M1 ? M1. The CASPT2/ANO potential energy curves of isomerization reactions were calculated as a function of HAlO bond angle. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011