Hydration of the HCl and NH3 molecules adsorbed on amorphous water–ice surface

Abstract

The interactions between HCl and NH3 molecules adsorbed on amorphous solid water (ASW) have been investigated by temperature-programmed time-of-flight secondary ion mass spectrometry (TP-TOF-SIMS). The NH4+ ion is sputtered predominantly from codeposited HCl and NH3 molecules on ASW due to collision-induced proton transfer reactions. The NH4+ yield is enhanced above 60K as a consequence of the formation of the NH4Cl molecule. The NH4+ yield steeply decays above 100K due to the hydration of the NH4Cl molecules, and the almost complete hydration occurs above 140K. The H/D exchange is induced rapidly between D2O and NH4Cl molecules above 120K. These behaviors strongly suggest that mobile water molecules exist on the surface above 100–120K.