PNNL

Abstract

Molecular beams were used to grow amorphous and crystalline H2O films and to dose HCl on their surface. The adsorption state of HCl on the films was probed with infrared spectroscopy. The spectral signature of hydronium ions was observed only when the HCl adlayer was in direct contact with the solid water films at temperatures as low as 20 K. The spectral signature of solid HCl (amorphous or crystalline) was identified only after saturation of the adsorption sites in the first layer or when deposited onto a rare gas spacer layer between the HCl and water film. The Zundel continuum is also clearly observed when the first HCl adlayer is in contact with the thin solid water films. These observations strongly support the spontaneous ionic dissociation of the first layer HCl adsorbed onto the ice surface, and the subsequent condensation of solid HCl, as observed by Parent and coworkers. [F. Bournel et al. Physical Review B 2002, 65, 2014041] using synchrotron-based electron spectroscopy