Potential Energy Curves, Transition Dipole Moments, and Franck-Condon Factors of the 12 Low-Lying States of BrO- Anion

Abstract

This work investigates the spectroscopic parameters, vibrational levels, and transition probabilities of 12 low-lying states, which are generated from the first dissociation limit, Br(²P_u) + O^-(²P_u), of the BrO^- anion. The 12 states are X¹Σ⁺, 2¹Σ⁺, 1¹Σ^-, 1¹Π, 2¹Π, 1¹Δ, a³Π, 1³Σ⁺, 2³Σ⁺, 1³Σ^-, 2³Π, and 1³Δ. The potential energy curves are calculated with the complete active-space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with Davidson modification. The dissociation energy D₀ of X¹Σ⁺ state is determined to be approximately 26876.44 cm^-1, which agrees well with the experimental one of 26494.50 cm^-1. Of these 12 states, the 2¹Σ⁺, 1¹Σ^-, 2¹Π, 1¹Δ, 1³Σ⁺, 2³Σ⁺, 2³Π, and 1³Δ states are very weakly bound states, whose well depths are only several-hundred cm^-1. The a³Π, 2³Π, and 1³Δ states are inverted and account for the spin-orbit coupling effect. No states are repulsive regardless of whether the spin-orbit coupling effect is included. The spectroscopic parameters and vibrational levels are determined. The transition dipole moments of 12-pair electronic states are calculated. Franck-Condon factors of a number of transitions of more than 20-pair electronic states are evaluated. The electronic transitions are discussed. The spin-orbit coupling effect on the spectroscopic parameters and vibrational properties is profound for all the states except for X¹Σ⁺, a³Π, and 1¹Π. The spectroscopic parameters and transition probabilities obtained in this paper can provide some powerful guidelines for observing these states in a proper spectroscopy experiment, in particular the states that have very shallow potential wells.