Direct-potential-fit analysis for the AΠ1u-XΣg+ system of Br2

Doppler-limited rovibrational absorption spectra of the A3Π_1u←X1Σg+ electronic transition of Br₂ are measured in the 12 072-14 249 cm^-1 region by a tone burst modulation method using a Ti:sapphire ring laser. P-, Q-, and R-branch lines belonging to the v' ← v″ = (2-16) ← (2-8) bands of ^79,79Br₂ and ^79,81Br₂, and the v' ← v″ = (2-5) ← 6 bands of ^81,81Br₂ are observed and assigned. Accurate analytic potential energy functions for the A³Π_1u and X1Σg+ states are determined from a combined-isotopologue direct-potential-fit analysis of these data together with all other available high quality data for the A and X states. This work also yields a slightly improved ground-state well depth D_e(X)=16056.875(2) cm^-1 and dissociation energy D₀(X)=15894.495(2) cm^-1 for ^79,79Br₂, and shows that the isotope shift of the A-X electronic transition energy Te81,81-Te79,79=-0.016(3) cm^-1 is likely mainly due to the isotopologue dependence of theX-state well depth.