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

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( 2 P u ) + O – ( 2 P u ), of the BrO – anion. The 12 states are X 1 Σ +, 2 1 Σ +, 1 1 Σ –, 1 1 Π, 2 1 Π, 1 1 Δ, a 3 Π, 1 3 Σ +, 2 3 Σ +, 1 3 Σ –, 2 3 Π, and 1 3 Δ. 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 D 0 of X 1 Σ + 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 2 1 Σ +, 1 1 Σ –, 2 1 Π, 1 1 Δ, 1 3 Σ +, 2 3 Σ +, 2 3 Π, and 1 3 Δ states are very weakly bound states, whose well depths are only several-hundred cm –1 . The a 3 Π, 2 3 Π, and 1 3 Δ 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 X 1 Σ +, a 3 Π, and 1 1 Π. 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.