Laser-induced fluorescence from resolved ro-vibrational levels (ν′, J′) of excited Br2A3Π(1u) has been observed, as the A–X transition. Excitation near 705 nm was carried out, using 10 ns pulses of narrow-band radiation (0.04 cm–1) with 250 µJ/pulse. Identification of the A–X ro-vibrational transitions was made through rotational combination differences and vibrational isotope splittings; new data for vibrational isotope splittings are reported.Lifetimes of the F– component of the (11,23) state of Br2(A) were measured as a function of pressure of Br2 and Ar as bath gases. The radiative lifetime τR of Br2(A) is reported to be (347 ± 50)µs (1σ). Vibrational energy transfer in collisions of Br2(A) with Br2(X) is very efficient, with kv 2.4 × 10–10 cm3 molecule–1 s–1 at 293 K. Vibrational-to-translational transfer in Br2(A)+ Ar collisions is about one order of magnitude slower. Electronic quenching of Br2(A) by Br2 and Ar is slow and an upper limit for quenching in Br2(A)+ Br2 collisions was determined, kQ⩽ 4˙7× 10–12 cm3 molecule–1 s–1.The interpretation of work by other workers on laser-induced fluorescence of excited IC1 A3Π(1) is discussed in the light of the present results on Br2.
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Clyne et al. (1980) studied this question.