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 τ_R of BrF (B) and to investigate vibrational transfer and quenching within the B-state manifold. The results give improved values for τ_R in the range 64.2 µs µS τ_R 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, k_Q,M, and for vibrational transfer, k_v,M, for collisions of BrF (B) with bath gases M = O₂, Cl₂, Ar, CHFCl₂ and HCl. Values of k_Q,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 k_v,M/cm³ molecule^–1 s^–1 were generally greater than those of k_Q,M and, as expected, increased with an increase in v′. For example, in the case of M = O₂, k_3,O2= 3.6 × 10^–11, which was one order of magnitude greater than the magnitude of k_Q,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.