Quantum-resolved dynamics of excited states. Part 6.—Radiative lifetime and collisional deactivation rates in BrF (B)

Abstract

Selected ro-vibrational levels (v′, J′) in electronically-excited BrF B3Π(0+) have been populated by absorption in the B–X system, using pulses of narrow-band dye laser radiation. The decay of laser-induced fluorescence in real time has been used to redetermine the radiative lifetime τR of BrF (B) and to investigate vibrational transfer and quenching within the B-state manifold. The results give improved values for τR in the range 64.2 µs µS τR 55.5 µs for 7 v′ 3.Broad-band wavelength-resolution of fluorescence and computer modelling were used to obtain rate constants at 293 K for quenching, kQ,M, and for vibrational transfer, kv,M, for collisions of BrF (B) with bath gases M = O2, Cl2, Ar, CHFCl2 and HCl. Values of kQ,M/cm3 molecule–1 s–1 ranged from ca. 1.2 × 10–11 for M = HCl, down to < 1 × 10–13 for M = Ar. Values of kv,M/cm3 molecule–1 s–1 were generally greater than those of kQ,M and, as expected, increased with an increase in v′. For example, in the case of M = O2, k3,O2= 3.6 × 10–11, which was one order of magnitude greater than the magnitude of kQ,O2, namely 2.6 × 10–12. Thus, in the case of BrF (B)+ O2 collisions, vibrational relaxation of the initial (v′, J′) state is much faster than electronic quenching.