Ab initio calculations for dipole-forbidden transitions in NBr: Radiative lifetimes of the b 1Σ + and a 1Δ states

Abstract

Spin-perturbed wavefunctions have been evaluated for the three lowest electronic states of NBr using the spin-orbit coupling Hamiltonian with MRD CI wavefunctions as the zeroth-order basis, and the radiative lifetimes of the a 1Δ and b 1Σ + states have been determined. Comparison is made with available experimental data. In the case of the b 1Σ +-X 3Σ 0,±1 − transition, the μ ∥ moment is found to be larger (by a factor of 7–11) than the μ ⊥ (whereby experiments indicate a factor of 15 or greater). In the case of the a 1Δ-X 3Σ ±1 − transition the calculated value is about two hundred and sixty times smaller than an experimental value reported in a gas-phase study, but it agrees quite well with the value determined in matrices. The zero-field splitting based on spin-orbit coupling alone has been calculated to be 11.3 cm −1, only 40–70% of the available experimental results. Finally comparison is made with the corresponding data for other nitrogen halides.