Quantum-resolved dynamics of excited states. Part 5.—The long-lived A3Π(1u) state of Br2

Abstract

Laser-induced fluorescence from resolved ro-vibrational levels (ν′, J′) of excited Br₂A³Π(1_u) 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 τ_R 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 k_v 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, k_Q 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.