Accurate calculations on 9 Λ-S and 28 Ω states of NSe radical in the gas phase: Potential energy curves, spectroscopic parameters and spin-orbit couplings

The PECs of 28 Ω states generated from 9 Λ-S states are studied using the CASSCF method, which is followed by the icMRCI and icMRCI + Q approaches. The 16Σ+, 14Σ+, 16Π, 24Π and 14Δ are found to be rather weakly bound states. And the 16Σ+, 14Σ+, 14Π and 16Π are found to be the inverted ones with the SO coupling added. The SO coupling is accounted for by the state interaction approach with the Breit-Pauli Hamiltonian. Core-valence correlation and scalar relativistic corrections are taken into account. All the PECs are extrapolated to the CBS limit. The variation with R of SO coupling constants is briefly discussed. The spectroscopic parameters of 9 Λ-S and 28 Ω states are evaluated. The splitting energy in the X2Π Λ-S state is determined as about 864.92 cm−1, which agrees favorably with the measurements of 891.80 cm−1. Moreover, other spectroscopic parameters of Λ-S and Ω states involved are also in excellent agreement with available measurements. It shows that the spectroscopic parameters reported here can be expected to be reliable predicted ones.