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(0_u⁺) are strongly dependent upon rotational and vibrational quantum numbers for the predissociated levels v′ > 12: τ^–1₀₀=τ^–1_R+k_v′J′(J′+ 1). Those states with zero rotation (J′= 0) are not predissociated and have lifetimes equal to the radiative lifetime, τ_R≃ 305 µs. The rotationally-dependent predissociation is assigned to a heterogeneous interaction (|ΔΩ|= 1) of the bound B³Π(0_u⁺) state and one or more ¹Π(1_u) 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: k_Cl2=(2.8 ± 0.1)× 10^–10 cm³ molecule^–1 s^–1.