Ionization and solvation of CsCl interacting with solid water

The interaction of CsCl with solid water, deposited on tungsten at 130 K, was investigated. Metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy [UPS(He I)] were applied to study the emission from the ionization of Cl(3p) and Cs(5p) and 1b(1), 3a(1), and 1b(2) of molecular water. Below a critical stoichiometry of about CsCl.6H(2)O the UPS spectra are quite similar to those for co-deposition of water and CsCl on tungsten, also studied here, and from chlorides solvated in liquid water inasmuch as the relative positions and intensities of the water and salt features are concerned. Very little emission from Cl(3p) and Cs(5p) is observed with MIES. We propose that CsCl dissociates, and the resulting ions become solvated in solid water. For supercritical stoichiometries Cs and Cl appear at the solid water surface and become accessible by MIES. CsCl-induced destruction of the water network takes place at the surface, and water molecules interact mainly with Cs and Cl, rather than with other water molecules. When subcritical films are heated above 135 K, the water-induced part of the spectrum changes its shape and becomes more gas phase like. Beyond 160 K no water can be detected with MIES. Above this temperature only Cs and Cl are found on the surface and desorb around 450 K. We have also studied water adsorption at 130 K on CsCl films. CsCl becomes solvated and migrates into the water overlayer.