Ab initio investigation on the low-lying electronic states of thallium bromide

Thirteen Λ-S states of TlBr molecule are calculated by the method of multireference configuration interaction (MRCI) plus Davidson correction (+Q), and the spectroscopic constants of these states are fitted. The dipole moment of thirteen Λ-S states are also included and analyzed in this calculation. Two bound states split into five Ω states with the SOC effect. The interaction between the molecular configurations of TlBr is analyzed with spin orbit coupling. Considering the forbidden transition, transition dipole moment with SOC effect is considered. On account of the accurate potential energy curves and the transition dipole moment, the Franck-Condon factors and radiative lifetime of the a³Π₀ ↔ Χ¹Σ₀⁺ transition are calculated. The feasibility of laser cooling of TlBr molecule is analyzed by comparing with the thallium compounds and the bromides of the group-IIIA.