Laser-induced fluorescence studies: the B–X transition of Cl2. Part 4.—Predissociation in the B state

Abstract

Laser-induced fluorescence has been used to determine the lifetimes of resolved ro-vibrational levels (v′, J′) in the predissociated parts of the excited B³Π(0⁺_u) manifold of ³⁵Cl³⁵Cl. Determinations were made over the ranges 13 ⩽v′⩽ 25 (except v′= 17, 20), and 0 ⩽J′⩽ 10.

The lifetimes (τ₀) showed strong variations with both rotational and vibrational quantum numbers, according to expression (II), 1/τ₀= 1/τ₀₀+k_v′J′(J′+ 1). (II) The mean value for the rotation-free lifetime τ₀₀ showed no significant dependence upon v′ in the range 13 ⩽v′⩽ 25.

The rotationally-dependent part of the predissociation in Cl₂(B) is assigned to a strong heterogeneous interaction (ΔΩ= 1) of the bound B³Π(0⁺_u) state and the unbound ¹Π(1_u) state. Values for k_v′(s^–1) varied from 7.1 × 10⁵ for v′= 13, down to 1.2 × 10⁵ for v′= 25. These values are much greater than those of k_v′ found previously for the similar heterogeneous predissociations in Br₂ and I₂, indicating a much stronger B³Π(0⁺_u)–¹Π(1_u) interaction in Cl₂.

The significance of these results in the spectroscopy and photochemistry of Cl₂ is discussed.