Diffusion of HDO into Single-Crystal H₂¹⁶O Ice Multilayers:  Comparison with H₂¹⁸O

Abstract

The diffusion of HDO into ultrathin single-crystal H2 16O ice multilayers was investigated using a novel combination of laser-induced thermal desorption (LITD) probing and isothermal desorption depth-profiling. The single-crystal hexagonal ice multilayers were grown epitaxially on a Ru(001) metal substrate, and the diffusion coefficients were measured perpendicular to the basal (0001) facet. The measured HDO diffusion coefficients ranged from D = (2.2 ± 0.3) × 10-16 to D = (3.9 ± 0.4) × 10-14 cm2/s over the temperature range 153−170 K. Arrhenius analysis of the temperature-dependent diffusion coefficients yielded a diffusion activation energy of E A = 17.0 ± 1.0 kcal/mol and a preexponential factor of D 0 = (4.2 ± 0.8) × 108 cm2/s. The similarity of the diffusion coefficients for HDO and H2 18O indicates that H/D exchange does not contribute significantly to HDO diffusion in ice. The agreement between the diffusion kinetics for HDO and H2 18O argues that the HDO diffusion occurs via a molecular transport mechanism. The large diffusion preexponentials for both HDO and H2 18O diffusion into the ultrathin ice multilayers also suggest that bulk transport properties in ice may be perturbed by close proximity to the ice surface.

Kinetics of OCN−formation from the HNCO + NH3solid-state thermal reaction

“…The activation energy of diffusion of HNCO within a NH 3 ice should be on the order of magnitude of a few 10 kJ mol −1 , the energy required to break few intermolecular hydrogen bonds (Park et al 2010). As a comparison the activation energy of the self-diffusion in bulk ice is E bulk a = 71±4 kJ mol −1 Livingston et al 1997). Therefore the diffusion of the molecules can be neglected between 8 and 60 K, on the time scale of our experiments, around 12 h typically.…”

Methane recovery from methane hydrate using pressurized CO2

“…According to the literature [27][28][29][30][31][32], solid diffusion has a large activation energy. In fact, several experimental investigations showed that the activation energy for diffusion of the H 2 O molecule in the bulk ice was in the range of 52-70 kJ/mol [27][28][29][30][31]. On the other hand, Wang et al measured the kinetics of the CH 4 hydrate formation from neutron diffraction and reported that the activation energy for the diffusion in the hydrate phase was 61.5 kJ/mol [32].…”

Probing Molecular Solids with Low-Energy Ions

“…At higher temperatures, diffusional mixing is easier to perform due to molecular motion and self-diffusion. The activation energy of diffusion measured at the surface was E a surface = 14 ± 2 kJ mol −1 , whereas in the bulk it was E a bulk = 71 ± 4 kJ mol −1 (110,111). Thus, diffusion at the surface is more significant than in bulk at 100-140 K. This finding indicates higher mobility on the surfaces and demonstrates that reaction preferentially occurs on ice surfaces, rather than in the bulk, at low temperatures.…”

“…One of the most-studied types of molecular solids consists of self-assembled monolayers (SAMs), which are highly ordered molecular films grown on a well-defined surface, usually Au (111). To provide a glimpse into the diverse phenomena that can be observed through LEIS, we present the surprising finding of multiple fluorine abstraction by a single W + ion collision event on a…”