Studies of BrCl by laser-induced fluorescence. Part 3.—Dynamics of quantum resolved levels in the excited B3Π(0+) state

Abstract

Laser-induced fluorescence has been used to determine the kinetics of decay of resolved ro-vibrational states of excited ⁸¹Br³⁵ClB³Π(0⁺) molecules. Fluorescence lifetimes have been measured as a function of J′(5 ⩽J′⩽ 60), v′(4 ⩽v′⩽ 6) and pressure of Cl₂(0.10 ⩽p⩽ 1.00 mTorr).

The mean value of the collision-free lifetime for the stable levels of ⁸¹Br³⁵Cl (B) was τ₀=(40.2 ± 1.8)µs, for 6 v′ 3. Although electronic quenching of the B-state of BrCl was slow, rapid vibrational energy transfer within this state was found to occur in collisions with Cl₂. This effect was manifested experimentally by a dependence upon v′ of the second-order rate constant for collisional deactivation of BrCl (B).

Predissociation of all rotational levels in the v′= 7 manifold was confirmed, and predissociation in v′= 6 has been observed for the first time as a shortening of lifetime of levels with J′⩽ 42. The collision-free lifetimes of these levels varied from τ₀= 8.8 µs for J′= 42, to τ₀= 4.3 µs for J′= 50, and showed a nearly linear dependence of 1/τ₀ upon J′(J′+ 1). Rotational levels up to at least J′= 70 in v′= 5 have been observed to be stable, indicating that the predissociation probably belongs to Herzberg's case I(c). New close limits for the ground state dissociation energy, namely D⁰₀(⁸¹Br³⁵Cl)=(17 934 ± 26) cm^–1, have been calculated, based on this observation.