Cl2p, O1s PSD–NEXAFS study of the adsorption of HCl on ice: a direct experimental evidence of the HCl ionization

We have used NEXAFS and photo-stimulated desorption (PSD)–NEXAFS spectroscopy at the O1s and at the Cl2p edges to study H2O and HCl ices, as well as the adsorption of HCl on water ice. The PSD–NEXAFS provides a clear fingerprint of the dangling OH bond at the water ice surface. We evidence the H–Cl fragmentation at the 2p→σ∗(H–Cl) excitation of condensed HCl. Last, we directly observe the ionization of HCl when adsorbed on H2O ice, both at the surface and after diffusion in the bulk of ice.