Reactive ion scattering from pure and mixed HCl, NH₃ and D₂O surfaces

Abstract

We have sampled the various species present on the condensed molecular layers of HCl, NH₃,D₂O and their mixtures by Cs⁺ reactive ion scattering (RIS) and low-energy sputtering. HCl and NH₃ exist in molecular states on pure molecular films, but the ammonium ion (NH₄⁺) is readily formed when HCl and NH₃ are co-deposited, by proton transfer from HCl to NH₃. Water is unnecessary for the proton transfer, although enhances it. In the presence of water, HCl ionizes first to form the hydronium ion (H₃O⁺), which subsequently transfers the proton to NH₃ to form NH₄⁺. This work demonstrates the capability of RIS for probing chemical species on condensed molecular surfaces and monitoring their reactions.