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

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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 D0 0(81Br35Cl)=(17 934 ± 26) cm–1, have been calculated, based on this observation.

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