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

摘要

Photofragment spectroscopy studies of the five alkali iodides have been done at 266 nm. For the four heavier iodides exclusive production of excited I2P1/2atoms 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 timehyphen;ofhyphen;flight distributions the following bond dissociation energies (D00) in kcalthinsp;molminus;1are determined: LiI 81.6plusmn;1.0; NaI 71.8plusmn;0.5; KI 76.2plusmn;0.5; RbI 75.3plusmn;0.5; CsI 79.7plusmn;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 60plusmn;4, 54plusmn;2, 51plusmn;2, and 51plusmn;2 for NaI,, KI, RbI, and CsI, respectively. The transition in LiI leading to ground state I atoms is 29percnt;plusmn;3percnt; parallel. Implications of these and other results for the nature of the first and second excited states of the alkali iodides are discussed.