Spin-orbit splitting in the X2Π, a4Π, B2Π and H2Π electronic states of the NS radical

Abstract

The potential energy curves (PECs) of ten Ω states (X2Π1 / 2,3 / 2, a4Π1 / 2,1 / 2,3 / 2,5 / 2, B2Π1 / 2,3 / 2 and H2Π1 / 2,3 / 2) generated from four Λ-S states (X2Π, a4Π, B2Π and H2Π) of the NS radical are studied in detail for the first time using an ab initio quantum chemical method. All the PEC calculations are performed for internuclear separations from 0.10 to 1.11 nm by the complete active space self-consistent field method followed by the internally contracted multireference configuration interaction approach with the Davidson modifications (MRCI + Q). The spin-orbit coupling (SO) effect is accounted for by the Breit- Pauli Hamiltonian. To discuss the effect on the energy splitting by the core-electron correlations, two all-electron basis sets, cc-pCVTZ and cc-pVTZ, are used for the SO coupling calculations. To improve the quality of the PECs, core-valence correlation and relativistic corrections are included. Core-valence correlation corrections are included with a cc-pCVTZ basis set. Relativistic correction calculations are carried out using the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. The spectroscopic parameters of four Λ-S states and ten Ω states are calculated. Excellent agreement is found between the present results and the measurements. Using the PECs obtained by the MRCI + Q/AV5Z + CV + DK + SO calculations, the G(υ), Bυ and Dυ are calculated for each vibrational state of each Ω state, and those of the first 30 vibrational states are reported for the X2Π1 / 2, X2Π3 / 2, B2Π1 / 2 and B2Π3 / 2 states of the 14N32S radical. The spectroscopic parameters of four Ω states of the a4Π and the G(υ), Bυ and Dυ of the X2Π1 / 2, X2Π3 / 2, B2Π1 / 2 and B2Π3 / 2 states reported here are expected to be reliable predicted results.