Oxygen K-Edge X-ray Absorption Fine Structure Studies of Vacuum-Deposited Ice Films

Multilayer ice films deposited on polycrystalline Au(111) substrates at 90 and 153 K under ultra-high-vacuum conditions are studied using O K-edge X-ray absorption fine structure spectroscopy in the surface-sensitive partial electron yield mode. Both near-edge and extended oscillatory fine structures are analyzed in combination with the theoretical real-space full-multiple-scattering simulations based on the FEFF8 code. The experimental data consistently indicate that the local structure of the near-surface regions in ice films at both substrate temperatures resembles that of high-density crystalline modifications of ice (e.g., ice II, ice III, or high-density amorphous ice). In addition, the ice films deposited at 153 K most probably contain a minor fraction of low-density cubic ice (Ic phase).