PNNL

Abstract

Isotopic exchange reactions in mixed D2O and H2O amorphous solid water films were investigated using reflection absorption infrared spectroscopy. Nanoscale films composed of 5% D2O in H2O were deposited on Pt(111) and graphene covered Pt(111) substrates using simultaneous co-dosing using two molecular beams. At 130 K, we find that the reaction is strongly dependent on the substrate with the H/D exchange occurring more rapidly on the Pt(111) surface than on graphene. At 140 K, the films eventually crystallize with the final products on the two substrates being primarily HOD on Pt(111) and a mixture of HOD and unreacted D2O on graphene. We demonstrate that the observed differences in reactivity on the two substrates is likely due to the formation of hydrogen ions at the Pt(111) surface that are not formed on graphene. Once formed the mobile protons move thorough the ASW overlayer to initiate the H/D exchange reaction.