title: 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.
abstract: The potential energy curves (PECs) of 28 Ω states generated from 9 Λ-S states (X(2)Π, 1(4)Π, 1(6)Π, 1(2)Σ(+), 1(4)Σ(+), 1(6)Σ(+), 1(4)Σ(-), 2(4)Π and 1(4)Δ) are studied for the first time using an ab initio quantum chemical method. All the 9 Λ-S states correlate to the first two dissociation limits, N((4)Su)+Se((3)Pg) and N((4)Su)+Se((3)Dg), of NSe radical. Of these Λ-S states, the 1(6)Σ(+), 1(4)Σ(+), 1(6)Π, 2(4)Π and 1(4)Δ are found to be rather weakly bound states. The 1(2)Σ(+) is found to be unstable and has double wells. And the 1(6)Σ(+), 1(4)Σ(+), 1(4)Π and 1(6)Π are found to be the inverted ones with the SO coupling included. 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. The spin-orbit coupling is accounted for by the state interaction approach with the Breit-Pauli Hamiltonian. The convergence of the present calculations is discussed with respect to the basis set and the level of theory. Core-valence correlation corrections are included with a cc-pCVTZ 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. The variation with internuclear separation of spin-orbit coupling constants is discussed in brief for some Λ-S states with one shallow well on each PEC. The spectroscopic parameters of 9 Λ-S and 28 Ω states are determined by fitting the first ten vibrational levels whenever available, which are calculated by solving the rovibrational Schrödinger equation with Numerov's method. The splitting energy in the X(2)Π Λ-S state is determined to be 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 here are also in fair agreement with available measurements. It demonstrates that the spectroscopic parameters reported here can be expected to be reliable predicted ones.
authors.affiliation: College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China. Electronic address: scattering@sina.com.cn.
authors.forename: Deheng
authors.initials: D
authors.lastname: Shi
authors.forename: Peiling
authors.initials: P
authors.lastname: Li
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Sun
authors.forename: Zunlue
authors.initials: Z
authors.lastname: Zhu
mesh_terms: D004583:Electrons; D005609:Free Radicals / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D011789:Quantum Theory; D012643:Selenium / Q000737:chemistry*; D013816:Thermodynamics; D014732:Vibration
chemical_list: D005609:Free Radicals; D005740:Gases; D012643:Selenium; D009584:Nitrogen
keywords: Core-valence correlation correction; Potential energy curve; Relativistic correction; Spectroscopic parameter; Spin-orbit coupling