Sodium Interacting with Amorphous Water Films at 10 and 100 K

Abstract

In the present study, we compare the adsorption of Na on amorphous D(2)O ice films, held at 10 and 100 K. OH, D(2)O, and Na are easily distinguished by their characteristic signatures in metastable impact electron spectroscopy (MIES). It is found that at 10 K substrate temperature the donation of 3sNa charge to the ice film, which is regarded as a precursor for water deprotonation, is significantly reduced relative to 100 K. This observation is discussed on the basis of recent theoretical work, suggesting that a rearrangement of the water molecules at the outermost water surface is the prerequisite for hydration/solvation of the 3sNa electron in the water ice bulk. The MIES spectra, showing spectral features from both OH and D(2)O, can be interpreted as reflecting the composition of the Na-water complexes in the near surface region. The relative intensity of the OH and D(2)O features is the same for 10 and 100 K. This finding suggests that two different sites for Na adsorption exist, one on the perfect water network and the other at OH dangling bond sites whereby, at 10 K, only the latter one leads to deprotonation of D(2)O. Finally, charge exchange phenomena observed when applying electron spectroscopies to ice films are discussed.