Kinetics of excited states of Br2using laser excitation. Part 2.—Radiative lifetime and collisional deactivation of the B3Π(0+u) state

Abstract

Selected ro-vibrational levels (ν′, J′) of the B³Π(0⁺ _u) excited state of Br₂ have been excited with a pulsed, narrow-band dye laser. The dynamics of collisional and non-collisional processes involving stable, non-predissociated levels of the ν′= 2 state have been investigated. Weak transitions of the (2–2) band have been identified for this purpose in the laser excitation spectrum of Br₂. Intensity anomalies in the excitation spectrum are discussed. The radiative lifetime τ_R of the (2, J′) states of Br₂(B) has been determined to be 12.4 ± 0.2 µs (1 σ); the agreement with data from the B–X absorption continuum is good. The rate constants k_Q,M(1 σ) for electronic quenching of Br₂(B, ν′= 2) by Br₂(X) and by Ar have been determined as k Q,Br₂ =(5.8 ± 0.3)× 10^–11 cm³ molecule^–1 s^–1 and k_Q,Ar=(1.7 ± 0.3)× 10^–11 cm³ molecule^–1 s^–1. Thus, the quenching efficiencies of Br₂(B) for both Br₂ and Ar are relatively low, as has been found previously for quenching of Cl₂(B), BrCl(B) and Br₂(A).