Probing icy surfaces with the dangling-OH-mode absorption: Large ice clusters and microporous amorphous ice

Abstract

Infrared absorption bands that have previously been assigned to vibrations of the dangling bonds (db) of water molecules at the surfaces of crystalline ice clusters and the micropores of amorphous ice have been investigated to determine their usefulness in probing molecular-level events at icy surfaces. This study has established that the db bands are sensitive to adsorption of gases at the cluster or micropore surfaces, and that reversible adsorption/desorption at the db sites is readily monitored spectroscopically. Consequently, energetics for the interactions with adsorbents such as H2 and N2 are potentially measurable. It has also been demonstrated, for both clusters and the micropores, that surface HOD molecules give unique db band positions, and that the intensities of the db bands are indicative of a strong preference of the surface HOD molecules to engage in deuterium bonding to the subsurface molecules. The unique positions of the HOD db bands also signals a potential for using isotopic-exchange data to monitor point-defect activity at icy surfaces.