Alkali halide photofragment spectra. II. Alkali bromide bond energies and excited state symmetries at 266 nm

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Abstract
Photofragment spectroscopy studies of the five alkali bromides at 266 nm show exclusive production of ground state 2P3/2 Br atoms in the photodissociation of LiBr and mixtures of ground and excited 2P1/2Br* atoms in the other bromides. Br*/Br branching ratios are 3.0, 2.5, 5.7, and 0.8 for NaBr, KBr, RbBr, and CsBr, respectively. From measured alkali atom recoil time‐of‐flight distributions the following bond energies (D00, kcal mol−1) are determined (all uncertainties ±1 kcal mol−1): LiBr‐99.2; NaBr‐85.9; KBr‐89.7; RbBr‐90.1; CsBr‐92.1. The recoil angular distributions indicate that the parallel and perpendicular transitions leading to Br and Br* atoms have approximately equal intensities for the four heavier bromides, while for LiBr 29% of the dipole strength to the single exit channel Li+Br is parallel polarized. These results are discussed in the context of simple one‐electron charge‐transfer model for the optical excitations, and are compared with similar studies on the alkali iodides.