Alkali halide photofragment spectra. I. Alkali iodide bond energies and excited state symmetries at 266 nm

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Abstract
Photofragment spectroscopy studies of the five alkali iodides have been done at 266 nm. For the four heavier iodides exclusive production of excited I2P1/2 atoms is found; for LiI, both ground and excited I atoms are produced, with ground state atoms favored two to one. From the measured alkali atom recoil time‐of‐flight distributions the following bond dissociation energies (D00) in kcal mol−1 are determined: LiI 81.6±1.0; NaI 71.8±0.5; KI 76.2±0.5; RbI 75.3±0.5; CsI 79.7±0.5. No evidence of dimer photodissociation is found. From recoil angular distributions the percentage parallel character of the transitions at 266 nm is found to be 60±4, 54±2, 51±2, and 51±2 for NaI,, KI, RbI, and CsI, respectively. The transition in LiI leading to ground state I atoms is 29%±3% parallel. Implications of these and other results for the nature of the first and second excited states of the alkali iodides are discussed.