General Trends for Bulk Diffusion in Ice and Surface Diffusion on Ice

Livingston, Frank E.; Smith, J. A.; George, Steven M.

doi:10.1021/jp014438c

Cited by 79 publications

(118 citation statements)

References 56 publications

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“…We estimate a dispersion of approximately 90% on the measured diffusion coefficients from five measurements performed on NH 3 at 117 K. The isothermal diffusion experiments are repeated at several temperatures for the different M molecules and the diffusion coefficients derived from fitting the experimental data with Fick's second law of diffusion are summarized in Table 3, along with measured thicknesses both in nm and in units of ML. These diffusion coefficient are consistent with those found by Livingston et al (2002).…”

Section: Analysis Using Fick's Second Law Of Diffusionsupporting

confidence: 92%

“…This rearrangement phenomenon can be related to the selfdiffusivity of ASW as discussed in Livingston et al (2002) and Smith (2000), and to the swapping mechanism developed by Öberg et al (2009) andFayolle et al (2011). We can consider that a restructuring amorphous solid has a diffusivity of vacancies toward the formation of a vacancy-free crystal.…”

Section: Influence Of the Asw Crystallization On The Diffusionmentioning

confidence: 97%

“…For the sake of comparison with diffusion coefficients derived from the Fick diffusion law, we can give the order of magnitude for the diffusion coefficients (in cm 2 s −1 ) using the rate constant (in s −1 ) in Table 4 derived from the Avrami equation using the approximate relation (Livingston et al 2002)…”

Section: Analysis Using An Avrami Equationmentioning

confidence: 99%

“…Livingston et al 2002 and references therein). Bulk diffusion is thought to be governed by a vacancy-sites migration mechanism with typical diffusion coefficients D from 10 −13 to 10 −10 cm 2 s −1 for a temperature range between 140 K and 200 K. However, extrapolating Livingston et al (2002) data to lower temperatures would lead to an impossibility for large molecules to diffuse in crystalline ice. For example CH 3 OH would have a diffusion coefficient of 10 −26 cm 2 s −1 at 100 K, and would diffuse across 100 nm in 10 4 years.…”

Section: Introductionmentioning

confidence: 99%

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Diffusion measurements of CO, HNCO, H₂CO, and NH₃in amorphous water ice

Mispelaer¹,

Theulé²,

Aouididi³

et al. 2013

A&A

115

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Context. Water is the major component of the interstellar ice mantle. In interstellar ice, chemical reactivity is limited by the diffusion of the reacting molecules, which are usually present at abundances of a few percent with respect to water. Aims. We want to study the thermal diffusion of H 2 CO, NH 3 , HNCO, and CO in amorphous water ice experimentally to account for the mobility of these molecules in the interstellar grain ice mantle. Methods. In laboratory experiments performed at fixed temperatures, the diffusion of molecules in ice analogues was monitored by Fourier transform infrared spectroscopy. Diffusion coefficients were extracted from isothermal experiments using Fick's second law of diffusion. Results. We measured the surface diffusion coefficients and their dependence with the temperature in porous amorphous ice for HNCO, H 2 CO, NH 3 , and CO. They range from 10 −15 to 10 −11 cm 2 s −1 for HNCO, H 2 CO, and NH 3 between 110 K and 140 K, and between 5-8 × 10 −13 cm 2 s −1 for CO between 35 K and 40 K. The bulk diffusion coefficients in compact amorphous ice are too low to be measured by our technique and a 10 −15 cm 2 s −1 upper limit can be estimated. The amorphous ice framework reorganization at low temperature is also put in evidence. Conclusions. Surface diffusion of molecular species in amorphous ice can be experimentally measured, while their bulk diffusion may be slower than the ice mantle desorption kinetics.

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Section: Analysis Using Fick's Second Law Of Diffusionsupporting

confidence: 92%

Section: Influence Of the Asw Crystallization On The Diffusionmentioning

confidence: 97%

Section: Analysis Using An Avrami Equationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Diffusion measurements of CO, HNCO, H₂CO, and NH₃in amorphous water ice

Mispelaer¹,

Theulé²,

Aouididi³

et al. 2013

A&A

115

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“…Within this grain-mantle system, we see that diffusion is central to correctly modelling both desorption and reactivity, as well as their competition. However, very few data exist on the diffusion of simple molecules in ice at low temperature (Livingston et al 2002), so diffusion is currently a major issue for modelling desorption on interstellar grains.…”

Section: Discussionmentioning

confidence: 99%

The desorption of H₂CO from interstellar grains analogues

Noble

Theulé

Mispelaer

et al. 2012

A&A

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Context. Much of the formaldehyde (H 2 CO) is formed from the hydrogenation of CO on interstellar dust grains, and is released in the gas phase in hot core regions. Radio-astronomical observations in these regions are directly related to its desorption from grains. Aims. We study experimentally the thermal desorption of H 2 CO from bare silicate surfaces, from water ice surfaces and from bulk water ice in order to model its desorption from interstellar grains. Methods. Temperature-programmed desorption experiments, monitored by mass spectrometry, and Fourier transform infrared spectroscopy are performed in the laboratory to determine the thermal desorption energies in: (i.) the multilayer regime where H 2 CO is bound to other H 2 CO molecules; (ii.) the submonolayer regime where H 2 CO is bound on top of a water ice surface; (iii.) the mixed submonolayer regime where H 2 CO is bound to a silicate surface; and (iv.) the multilayer regime in water ice, where H 2 CO is embedded within a H 2 O matrix. Results. In the submonolayer regime, we find the zeroth-order desorption kinetic parameters ν 0 = 10 28 mol cm −2 s −1 and E = 31.0 +/− 0.9 kJ mol −1 for desorption from an olivine surface. The zeroth-order desorption kinetic parameters are ν 0 = 10 28 mol cm −2 s −1 and E = 27.1 +/− 0.5 kJ mol −1 for desorption from a water ice surface in the submonolayer regime. In a H 2 CO:H 2 O mixture, the desorption is in competition with the H 2 CO + H 2 O reaction, which produces polyoxymethylene, the polymer of H 2 CO. This polymerization reaction prevents the volcano desorption and co-desorption from happening. Conclusions. H 2 CO is only desorbed from interstellar ices via a dominant sub-monolayer desorption process (E = 27.1 +/− 0.5 kJ mol −1 ). The H 2 CO which has not desorbed during this sub-monolayer desorption polymerises upon reaction with H 2 O, and does not desorb as H 2 CO at higher temperature.

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