Helium Diffusion through<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi mathvariant="normal">O</mml:mi></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi mathvariant="normal">D</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi mathvariant="normal">O</mml:mi></mml:math>Amorphous Ice: Observation of a Lattice Inverse Isotope Effect

Daschbach, John L.; Schenter, Gregory K.; Ayotte, Patrick; Smith, R. Scott; Kay, Bruce D.

doi:10.1103/physrevlett.92.198306

Cited by 12 publications

(4 citation statements)

References 13 publications

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“…The calculated values of D and τ have a direct relation with the efficiency of the hydrogen recombination at the grain surface, as discussed in . At warmer temperatures, D is expected to increase exponentially, as found experimentally and theoretically (Ikeda‐Fukazawa et al 2002; Daschbach et al 2004) in the case of He diffusion in ice. Those values are lower by orders of magnitude than those found here at low temperatures, because the earlier calculations and experiments were performed to study the diffusion of He inside the ice rather than at the ice surface, which is expected to be much higher.…”

Section: Resultssupporting

confidence: 59%

Hydrogen adsorption and diffusion on amorphous solid water ice

Al-Halabi

Dishoeck

2007

Monthly Notices of the Royal Astronomical Society

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Results of classical trajectory calculations on the adsorption of H atoms to amorphous solid water (ASW) ice, at a surface temperature T s of 10 K are presented. The calculations were performed for incidence energies E i ranging from 10 to 1000 K, at random incidence. The adsorption probability P s can be fitted to a simple decay function: P s = 1.0e −E i (K )/300 . Our calculations predict similar adsorption probabilities for H atoms to crystalline and ASW ice, although the average binding energy E b of the trapped H atoms calculated for ASW of 650 ± 10 K is higher than that found for crystalline ice of 400 ± 5 K. The binding energy distributions were fitted to Gaussian functions with full width half-maximum of 111 and 195 K for crystalline and amorphous ice surfaces, respectively. The variation of the H atom binding sites in the case of the ASW surface leads to broadening of the distribution of E b compared to that of crystalline ice. We have also calculated the 'hot-diffusion' distance travelled by the impinging atom over the surface before being thermalized, which is found to be about 30 Å long at E i = 100 K and increases with E i . The diffusion coefficient D of thermally trapped H atoms is calculated to be 1.09 ± 0.04 × 10 −5 cm 2 s −1 at T s = 10 K. The residence time τ of H atoms adsorbed on ASW is orders of magnitude longer than that of H atoms adsorbed on crystalline ice for the same ice T s , suggesting that H 2 formation on crystalline and non-porous ice is quite limited compared to that on porous ice. This is in good agreement with the results of experiments on H 2 formation on porous and non-porous ASW surfaces. At low T s , the long values of τ , the high values of D and the large hot distance travelled on the ASW surface before trapping the impinging H atom ensure that Langmuir-Hinshelwood and hot-atom mechanisms for H 2 formation will be effective. The data presented here will be important ingredients for models to describe the formation of H 2 on interstellar ices and reactions of H atoms with other species at the ice surface.

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Section: Resultssupporting

confidence: 59%

Hydrogen adsorption and diffusion on amorphous solid water ice

Al-Halabi

Dishoeck

2007

Monthly Notices of the Royal Astronomical Society

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“…64 Second, the diffusion rate of helium in D 2 O ice was shown to be higher than in H 2 16 O ice because of the lower vibrational frequency of the O-D bond, which allows for easier hopping of the gas molecule from site to site. 59 Hydrates have also been shown to concentrate D 2 O by approximately 2 mol %, a greater extent than for H 2 18 O. 61,62 Finally, the hydrate equilibrium temperature for D 2 O-methane hydrate is approximately 2.5 K higher than for H 2 O-methane hydrate.…”

Section: Resultsmentioning

confidence: 98%

“…In addition, the diffusion rate of helium in ice Ih formed from H 2 16 O and H 2 18 O was found to be similar. 59 16 O, and it is therefore unclear how the diffusion rates would compare in a hydrate lattice. 64 Second, the diffusion rate of helium in D 2 O ice was shown to be higher than in H 2 16 O ice because of the lower vibrational frequency of the O-D bond, which allows for easier hopping of the gas molecule from site to site.…”

Section: Resultsmentioning

confidence: 99%

In Situ Studies of the Mass Transfer Mechanism across a Methane Hydrate Film Using High-Resolution Confocal Raman Spectroscopy

et al. 2009

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Hydrate films typically form at gas-water interfaces where the concentrations of guest and host molecules are the highest. Once formed, the films provide a significant mass transfer barrier to further hydrate formation. However, controversy exists about whether it is the transport through the crystal film of the guest or the host (water) molecule that controls further hydrate growth. In this study, methane hydrate films were formed at a gas-water interface, and the gas and water phases were then replaced by isotopic tracers. The concentration profiles of the tracers across the hydrate films were studied over time using confocal Raman spectroscopy in order to determine the relative mobility of guest and host molecules within hydrate film. The films were found to contain gas-filled pores, which provided pathways for gas migration. These pores annealed over time, increasing the mass transfer resistance. The results indicate that the host water molecules are the most mobile species in the hydrate phase, and that hydrate growth is controlled by the movement of water within the hydrate film.

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“…4 In their model, the sticking probability is related to the time available for steering of the incident molecule into a favorable orientation for adsorption. Since the interaction potential of the two isotope-ices towards the incident D 2 18 they could also play a role in the sticking dynamics of water on ice.…”

Section: Resultsmentioning

confidence: 99%

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

Hundt

Bisson

Beck

2012

The Journal of Chemical Physics

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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.

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Helium Diffusion throughH2OandD2OAmorphous Ice: Observation of a Lattice Inverse Isotope Effect

Cited by 12 publications

References 13 publications

Hydrogen adsorption and diffusion on amorphous solid water ice

Hydrogen adsorption and diffusion on amorphous solid water ice

In Situ Studies of the Mass Transfer Mechanism across a Methane Hydrate Film Using High-Resolution Confocal Raman Spectroscopy

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

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