Laser-induced fluorescence studies: the B–X transition of Cl2. Part 5.—Radiative lifetime of the B state

Abstract

A redetermination of the radiative lifetime of the long-lived B³Π(O_u⁺)state of ³⁵Cl³⁵Cl is described. Pulses of narrow-band radiation from a scanning dye laser (> 1 mJ pulse^–1) were used to excite the v′= 5, J′= 16 state of Cl₂(B). Decay of fluorescence in real time was used to determine τ_R for the v′= 5 state: τ_R=(305 ± 15)µs (1σ). Reasons for error in previous work are discussed. The long radiative lifetime of Cl₂(B) is consistent with estimates based on absorption coefficient measurements in the ultraviolet continuum of Cl₂.

The low efficiency at 298 K of electronic self-quenching of Cl₂(B) is confirmed, with k_Q,Cl2=(6.4 ± 0.6)× 10^–12 cm³ molecule^–1 s^–1. Quenching by Ar, N₂ and O₂ also is inefficient, with k_Q,Ar⩽ 4.9 × 10^–12, k_Q,N2⩽ 1 × 10^–11 and k_Q,O2⩽ 1 × 10^–11 cm³ molecule^–1 s^–1.