Spectroscopic parameters, vibrational levels, transition dipole moments and transition probabilities of the 9 low-lying states of the NCl+ cation

Abstract

This work calculates the potential energy curves of 9 Λ-S and 28Ω states of the NCl⁺ cation. The technique employed is the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson correction. The Λ-S states are X²Π, 1²Σ⁺, 1⁴Π, 1⁴Σ⁺, 1⁴Σ^-, 2⁴Π, 1⁴Δ, 1⁶Σ⁺, and 1⁶Π, which are yielded from the first two dissociation channels of NCl⁺ cation. The Ω states are generated from these Λ-S states. The 1⁴Π, 1⁴Δ, 1⁶Σ⁺, and 1⁶Π states are inverted with the spin-orbit coupling effect included. The 1⁴Σ⁺, 1⁶Σ⁺, and 1⁶Π states are very weakly bound, whose well depths are only several-hundredcm^-1. One avoided crossing of PECs occurs between the 1²Σ⁺ and 2²Σ⁺ states. To improve the quality of potential energy curves, core-valence correlation and scalar relativistic corrections are included. The potential energies are extrapolated to the complete basis set limit. The spectroscopic parameters and vibrational levels are calculated. The transition dipole moments are computed. The Franck-Condon factors, Einstein coefficients, and radiative lifetimes of many transitions are determined. The spectroscopic approaches are proposed for observing these states according to the transition probabilities. The spin-orbit coupling effect on the spectroscopic and vibrational properties is evaluated. The spectroscopic parameters, vibrational levels, transition dipole moments, as well as transition probabilities reported in this paper could be considered to be very reliable.

Keywords: Electric dipole transition; Franck-Condon factor; Potential energy curve; Spectroscopic parameter; Spin-orbit coupling; Transition probability.