Structural relaxation rates near the ice surface: Basis for separation of the surface and subsurface spectra

A differential in the relaxation rates of the ice surface and subsurface during Ostwald ripening near 138 K is the basis for a new approach to determination of the separate surface and subsurface vibrational spectra of ice nanocrystals. The resulting FT-ir spectrum of the ice subsurface matches that previously obtained from adsorbate-induced relaxation of the subsurface, confirming both the form of the surface and subsurface spectra, and the disordered nature of the surface of the nanocrystals. From these data, together with the results of simulation studies, ice emerges as the only molecular crystalline substance for which the surface and subsurface spectra are known and assigned. Semiquantitative rates of the structural relaxations near the surface, for bare ice and ice coated with the adsorbate SO2, have also been determined. Finally, spectral data are presented that track the insertion of SO2 into the vulnerable strained H bonds common to simulated structures of the ice surface. (C) 1997 American Institute of Physics.