Multireference configuration interaction study of the 21 low-lying states of the OF radical

Abstract

This paper calculated the potential energy curves of 21Λ-S and 42Ω states of the OF radical. The 21Λ-S states were the X2Π, A2Σ−, B2Σ−, C2Δ, D2Σ+, E2Σ+, 22Π, a4Σ−, b4Δ, 24Σ−, 14Σ+, 14Π, 24Π, 32Σ+, 32Σ−, 32Π, 42Π, 52Π, 22Δ, 32Δ, and 12Φ, which arose from the first two dissociation limits. The 42Ω states were generated from these Λ-S states. All the potential energy curves were calculated with the CASSCF method, which was followed by the icMRCI+Q approach. The 14Π, 24Π, 22Π, 42Π, 52Π, 32Σ+, and 32Δ states were repulsive whether the spin-orbit coupling effect included or not, but the A2Σ−, D2Σ+, 32Σ−, 22Δ, and 12Φ states became repulsive with the spin-orbit coupling effect included. Only the 16Ω states were bound. With the spin-orbit coupling effect accounted for, the X2Π state was inverted among the bound states; the X2Π, a4Σ−, and E2Σ+ states were strongly bound; and the 32Π, b4Δ, B2Σ−, C2Δ, 24Σ−, and 14Σ+ states were very weakly bound. The spectroscopic and vibrational properties were determined. Franck–Condon factors of some transitions were evaluated. The spin-orbit coupling effect on the spectroscopic parameters and vibrational properties was discussed. It is very difficult to explore the X2Π, a4Σ−, and E2Σ+ states by observing the electronic transitions between them because all these strong transitions originating only from the highly-vibrational states of the X2Π or a4Σ− state. It is also very hard to detect the 32Π, b4Δ, B2Σ−, C2Δ, 24Σ−, and 14Σ+ states by observing the transitions originating from these states, because these states are very weakly bound and unstable, though some transitions originating from them are very strong. These results can well explain why the OF radical is very difficult to detect in a spectroscopic experiment by observing the electronic transitions between different states.