Laser-induced fluorescence studies: the B–X transition of Cl2. Part 6.—Rotationally-dependent predissociation

Abstract

The collision-free lifetimes of ro-vibrational levels (v′,J′) of excited Cl2B3Π(0u+) are strongly dependent upon rotational and vibrational quantum numbers for the predissociated levels v′ > 12: τ–100=τ–1R+kv′J′(J′+ 1). Those states with zero rotation (J′= 0) are not predissociated and have lifetimes equal to the radiative lifetime, τR≃ 305 µs. The rotationally-dependent predissociation is assigned to a heterogeneous interaction (|ΔΩ|= 1) of the bound B3Π(0u+) state and one or more 1Π(1u) states. Homogeneous predissociation (|ΔΩ|= 0), which is forbidden by selection rules, is not present in the B state of Cl2.The lifetime of the J′= 0 state shows a strong dependence on pressure of Cl2, which is interpreted in terms of rapid collisional pre-dissociation and rotational energy transfer into states J′ 1 which have negligible fluorescence quantum yields. The rate constant for overall transfer out of the v′= 13 state was found to be: kCl2=(2.8 ± 0.1)× 10–10 cm3 molecule–1 s–1.