Photoionization of High-Temperature Vapors. V. Cesium Halides; Chemical Shift of Autoionization

Abstract

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 $D_0$ obtained are CsCl, 105.6 ± 1.6 kcal/mole; CsBr, 96.2 ± 1 kcal/mole; CsI, 82.3 ± 1 kcal/mole. For $D_0(\mathrm{CsF})$ , the interpretation is in doubt. The dissociation energies of the molecular ions CsBr⁺ and CsI⁺ have also been measured, as have the heats of formation of Cs₂F⁺, Cs₂Cl⁺, and Cs₂Br⁺. 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 ${\text{(5p)}}^6{\text{6s\hspace{0.17em}→\hspace{0.17em}(5p)}}^5{\text{(6s)}}^2$ 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 CsI, respectively. These peaks are also present in the ionization efficiency curves of the dimer ions. Some consequences of these results are discussed.