Fast thermal desorption spectroscopy study of morphology and vaporization kinetics of polycrystalline ice films

Fast thermal desorption spectroscopy was used to investigate the vaporization kinetics of thin (50-100 nm) H2O18 and HDO tracer layers from 2-5 mu m thick polycrystalline H2O16 ice films at temperatures ranging from -15 to -2 degrees C. The isothermal desorption spectra of tracer species demonstrate two distinct peaks, alpha and beta, which we attribute to the vaporization of H2O18 initially trapped at or near the grain boundaries and in the crystallites of the polycrystalline ice, respectively. We show that the diffusive transport of the H2O18 and HDO tracer molecules in the bulk of the H2O16 film is slow as compared to the film vaporization. Thus, the two peaks in the isothermal spectra are due to unequal vaporization rates of H2O18 from grain boundary grooves and from the crystallites and, therefore, can be used to determine independently the vaporization rate of the single crystal part of the film and rate of thermal etching of the film. Our analysis of the tracer vaporization kinetics demonstrates that the vaporization coefficient of single crystal ice is significantly greater than those predicted by the classical vaporization mechanism at temperatures near ice melting point. We discuss surface morphological dynamics and the bulk transport phenomena in single crystal and polycrystalline ice near 0 degrees C. (c) 2006 American Institute of Physics.