Surface and bulk diffusion of HDO on ultrathin single-crystal ice multilayers on Ru(001)

Abstract

The kinetics of HDO surface and bulk diffusion on ultrathin (25–192 BL; 90–700 Å) single-crystal H216O ice multilayers were studied using a combination of laser-induced thermal desorption (LITD) probing and isothermal desorption depth-profiling. The single-crystal hexagonal ice multilayers were grown epitaxially on a single-crystal Ru(001) metal substrate with the basal (001) facet of ice parallel to the Ru(001) surface. HDO surface diffusion on the single-crystal ice multilayer was not observed within the resolution of the LITD experiment at T=140 K. These LITD surface diffusion experiments yielded an upper limit to the HDO surface diffusion coefficient of Ds⩽1×10−9 cm2/s at T=140 K. The bulk diffusion coefficients were measured along the c axis of the hexagonal ice crystal which is perpendicular to the (001) plane. HDO was observed to diffuse readily into the underlying H216O ice multilayer. The measured HDO bulk diffusion coefficients ranged from D=2.2(±0.3)×10−16 cm2/s to D=3.9(±0.4)×10−14 cm2/s over the temperature range from 153 to 170 K. The HDO bulk diffusion coefficients were measured for H216O thicknesses of 25–192 BL (1 BL=1.06×1015 molecules/cm2) and initial HDO adlayer thicknesses of 2–9 BL. The HDO bulk diffusion was independent of H216O film thickness and initial HDO coverage. Arrhenius analysis of the temperature-dependent bulk diffusion coefficients yielded a diffusion activation energy of EA=17.0±1.0 kcal/mol and a diffusion preexponential of Do=4.2(±0.8)×108 cm2/s. Compared with extrapolations from macroscopic diffusion kinetics obtained earlier at temperatures close to the melting point, these bulk diffusion coefficients are larger and may reflect the perturbation of the ultrathin ice films induced by the nearby interfaces. The differences between these HDO diffusion kinetics and recently measured kinetics for H218O indicate that H/D exchange and molecular transport make comparable contributions to the HDO diffusion coefficient.

Structure, spectra, and mobility of low‐pressure ices: Ice I, amorphous solid water, and clathrate hydrates at T < 150 K

“…However, elegant laser desorption methods, combined with nonequilibrium distributions of water isotopomers, have been used to gauge the self-diffusion of water molecules in ice thin films in the 153-170 K range [Livingston et al, 1998]. These measurements showed a very rapid rise in mobility in this ran•e corresponding to a high activation energy (17.0 kcal mol').…”

Measuring the specific surface area of snow with X-ray tomography and gas adsorption: comparison and implications for surface smoothness

“…The surface diffusion constant D s has been determined in the past in a number of different experiments, but the results depend heavily on the method and on the temperature range of the measurement (Mizuno and Hanafusa, 1987;Brown and George, 1996;Livingston et al, 1997;Jung et al, 2004). Here, we use the work of Mizuno and Hanafusa (1987), since they measured the properties in the quasi liquid layer on a collection of small ice beads at temperatures close to the melting point, which resembles the situation in snow.…”

A new modeling tool for the diffusion of gases in ice or amorphous binary mixture in the polar stratosphere and the upper troposphere

“…During the last decade, new infrared-laser resonant desorption (LRD) techniques have been employed to derive diffusion coefficients by depth profiling of ice films George, 1999, 2001;Livingston et al, 1997Livingston et al, , 1998Livingston et al, , 2000Livingston et al, , 2002Krasnopoler and George, 1998). These measurements revealed two different rate categories for bulk diffusion in ice.…”