The sticking probability of D2O-water on ice: Isotope effects and the influence of vibrational excitation

Abstract

The present study measures the sticking probability of heavy water (D 2 O) on H 2 O-and on D 2 O-ice and probes the influence of selective OD-stretch excitation on D 2 O sticking on these ices. Molecular beam techniques are combined with infrared laser excitation to allow for precise control of incident angle, translational energy, and vibrational state of the incident molecules. For a translational energy of 69 kJ/mol and large incident angles (θ ≥ 45 • ), the sticking probability of D 2 O on H 2 O-ice was found to be 1% lower than on D 2 O-ice. OD-stretch excitation by IR laser pumping of the incident D 2 O molecules produces no detectable change of the D 2 O sticking probability (<10 −3 ). The results are compared with other gas/surface systems for which the effect of vibrational excitation on trapping has been probed experimentally.

Water dissociation on Ni(100) and Ni(111): Effect of surface temperature on reactivity

“…On the contrary, experimental study on D 2 O water on ice shows no change in the sticking probability with vibrational excitation which may be due to lack of vibrational-translational coupling in the ice surface and hence to the insensitivity of trapping to vibrational excitation. 22 It is observed that all the above investigations were carried out under the static surface approximation in which metal surface is assumed to be rigid. Theory and experiments have shown that surface temperature has profound effect on reaction probability of light molecules like H 2 23 and also on heavier molecules like methane 24 and N 2 .…”

Isotope effects on the photodesorption processes of X2O (X = H,D) and HOD ice

“…In a different kind of experiment, Hundt et al 30 = 10, 20, 30, 60, and 90 K. Some of these results were taken from previous MD simulations by Arasa et al 12 Also, MD simulations for HOD* in an H 2 O amorphous ice system have been performed. This paper is set up as follows.…”

“…To investigate the isotope effects on the photodesorption processes of X 2 O (X = H,D) ice, molecular dynamics calculations have been performed on the ultraviolet photodissociation of an H 2 O or a D 2 O molecule in an H 2 O or a D 2 O amorphous ice surface, and on HOD photodissociation in an H 2 O amorphous ice surface, where the photodissociated molecules were located in the top four or five monolayers at ice temperatures of 10,20,30,60, and 90 K. Three photodesorption processes can occur upon X 2 O photodissociation: X atom photodesorption, OX radical photodesorption, and X 2 O (or HOD) molecule photodesorption. X 2 O (or HOD) photodesorption can occur after recombination of X and OX, or after an energetic X atom photofragment kicks a surrounding X 2 O molecule from the ice surface.…”

Differential Condensation of Methane Isotopologues Leading to Isotopic Enrichment under Non-equilibrium Gas–Surface Collision Conditions

“…This model does not account for the density of states of the film or the internal modes of the molecule, as discussed later. These contributions can influence sticking probabilities. , Because of the role of these molecular degrees of freedom, complex and multi-phonon interactions , between the surface and the incident projectiles CH 4 film and CD 4 clearly need to be taken into consideration, as they are in the MD simulations shown herein.…”

“…When doing so, we see the same effect in the condensed mixed film, supporting an isotopic enrichment of the heavier isotope. Because the Baule model 74 does not accurately represent this condensed phase system due to its molecular complexity, we propose that enhanced multi-phonon interactions attributable to the film’s phonon and rovibrational densities of states and inelastic cross sections including intermolecular energy exchange between the incident CD 4 projectile and the CH 4 film allow for more efficacious gas–surface energy transfer.…”