Accurate calculations on the 22 electronic states and 54 spin-orbit states of the O2 molecule: Potential energy curves, spectroscopic parameters and spin-orbit coupling

Abstract

The potential energy curves (PECs) of 54 spin-orbit states generated from the 22 electronic states of O2 molecule are investigated for the first time for internuclear separations from about 0.1 to 1.0nm. Of the 22 electronic states, the X3Σg-, A′3Δu, A3Σu+, B3Σu-, C3Πg, a1Δg, b1Σg+, c1Σu-, d1Πg, f1Σu+, 15Πg, 13Πu, 23Σg-, 15Σu-, 21Σu- and 21Δg are found to be bound, whereas the 15Σg+, 25Σg+, 11Πu, 15Δg, 15Πu and 21Πu are found to be repulsive ones. The B3Σu- and d1Πg states possess the double well. And the 13Πu, C3Πg, A′3Δu, 15Δg and 25Σg+ states are the inverted ones when the spin-orbit coupling is included. The PEC calculations are done by the complete active space self-consistent field (CASSCF) method, which is followed by the internally contracted multireference configuration interaction (icMRCI) approach with the Davidson correction. Core-valence correlation and scalar relativistic corrections are taken into account. The convergence of present calculations is evaluated with respect to the basis set and level of theory. The vibrational properties are discussed for the 15Πg, 13Πu, d1Πg and 15Σu- states and for the second well of the B3Σu- state. The spin-orbit coupling effect is accounted for by the state interaction method with the Breit-Pauli Hamiltonian. The PECs of all the electronic states and spin-orbit states are extrapolated to the complete basis set limit. The spectroscopic parameters are obtained, and compared with available experimental and other theoretical results. Analyses demonstrate that the spectroscopic parameters reported here can be expected to be reliably predicted ones. The conclusion is obtained that the effect of spin-orbit coupling on the spectroscopic parameters are small almost for all the electronic states involved in this paper except for the 15Σu-, 15Πg and 13Πu.