Kinetics of excited states of Br2 using laser excitation. Part 1 .—System description and rotationally-dependent lifetimes in Br2(B)

Abstract

A pressure-tuned narrow-band day laser is described. This instrument was used to provide linear scans, free of mode hops, of selected parts of the Br₂(B–X) band spectrum in laser-induced fluorescence. Resolution was Doppler limited.

Measurements of collision-free lifetimes τ₀ of Br₂(B) excited molecules were made over a range of rotational states J′, for several vibrational states 23 v′ 11. A strong dependence of Γ₀= 1/τ₀ upon J′, was found, which was attributed to a heterogeneous predissociation of the emitting B³Π(0⁺_u) state. The results gave a good fit to the relationship, Γ₀=Γ_R+k_v′J′(J′+ 1). The mean value of the radiative, rotation-free lifetime (τ_R= 1/Γ_R) was 8.1 µs for 24 v′ 11.

The results show that virtually all band absorption of Br₂ between 540 and 590 nm leads to formation of ²P+²P bromine atoms via predissociation.