Interaction of HCl with crystalline and amorphous ice: Implications for the mechanisms of ice‐catalyzed reactions

Abstract

The interaction of HCl with ice under ultrahigh vacuum has been studied using temperature programmed desorption and single reflection Fourier transform infrared spectroscopy. Both amorphous and crystalline ice were investigated. At 120 K, HCl is initially absorbed by ice to form a stoichiometric hydrate phase identified as HCl · 6H2O. Upon completion of the bulk phase, HCl is adsorbed to the surface. This initial HCl adsorption probability on crystalline ice is ≈60% of that on amorphous ice. Furthermore, the adsorption probability on crystalline ice decreases more rapidly with increasing HCl uptake. As a result, HCl · 6H2O is more rapidly formed in amorphous ice. The difference in adsorption probabilities is tentatively attributed to a lower coverage of dangling OH groups at the crystalline ice surface.