Accurate ab initio study on the A2Π, 14Σ+, 14Π, 24Π and 16Σ+ electronic states of AlO radical including spin–orbit coupling

Abstract

The potential energy curves (PECs) of 15 Ω states generated from five Λ–S states (A2Π, 14Σ+, 14Π, 24Π and 16Σ+) of AlO radical are studied in detail using high level ab initio quantum chemical method for the first time. All the PEC calculations are made by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson modification (MRCI+Q). The spin–orbit coupling effect is included by the Breit–Pauli Hamiltonian with the aug-cc-pCVTZ basis set. Convergent behavior is discussed and excellent convergence has been observed with respect to the basis sets and level of theory. To improve the quality of PECs, core–valence correlation and scalar relativistic corrections are taken into account. Core–valence correlation corrections are included employing a cc-pCVQZ basis set. Scalar relativistic corrections are calculated by the third-order Douglas–Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. All the PECs are extrapolated to the complete basis set limit by the total-energy extrapolation scheme. With these PECs including all the corrections used here, on the one hand, the spectroscopic parameters of all the Λ–S and Ω states are calculated, which are in reasonable agreement with the experimental and other theoretical results; on the other hand, the vibrational levels and inertial rotation constants of X2Σ+, A2Π, B2Σ+ Λ–S states as well as A2Π3/2 and A2Π1/2 Ω states are determined, which also agree well with the measurements. The vibrational levels and inertial rotation constants of A2Π3/2 and A2Π1/2 Ω states as well as the spectroscopic parameters of four Λ–S states (14Σ+, 14Π, 24Π and 16Σ+) and their corresponding 13 Ω states can be expected to be reliable predicted ones.