PHOTOIONIZATION OF HIGH-TEMPERATURE VAPORS .V. CESIUM HALIDES - CHEMICAL SHIFT OF AUTOIONIZATION

From the thresholds for photodissociative ionization of cesium halide molecules, results have been obtained for the dissociation energies of the diatomic molecules. The values of Da obtained are CsCl, 105.6± 1.6 kcal/mole; CsBr, 96.2±1 kcal/mole; Csl, 82.3±1 kcal/mole. For Do(CsF), the interpretation is in doubt. The dissociation energies of the molecular ions CsBr+ and Csl+ have also been measured, as have the heats of formation of CszF+, Cs2Cl+, and Cs 2Br+. Several autoionization peaks have been observed in the ionization efficiency curves of the cesium halides, somewhat displaced in energy from their positions in atomic cesium. In particular, the (5p) 66s→(5p)5(6s)2 transition, which occurs at 12.306 eV in atomic cesium, is shifted to 12.1, 12.4, 12.5, and 12.6 eV, for CsF, CsCl, CsBr, and Csl, respectively. These peaks are also present in the ionization efficiency curves of the dimer ions. Some consequences of these results are discussed.