Direct-potential-fit analysis for the system of Br2

Doppler-limited rovibrational absorption spectra of the A 3 Π 1 u ← X 1 Σ g + 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 A3Π1u and X 1 Σ g + 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 D 0 ( X ) = 15894.495 ( 2 ) cm - 1 for 79,79Br2, and shows that the isotope shift of the A–X electronic transition energy T e 81 , 81 – T e 79 , 79 = - 0.016 ( 3 ) cm - 1 is likely mainly due to the isotopologue dependence of theX-state well depth.