Adsorption, desorption, and diffusion of nitrogen in a model nanoporous material. I. Surface limited desorption kinetics in amorphous solid water

Zubkov, Tykhon; Smith, R. Scott; Engstrom, Todd; Kay, Bruce D.

doi:10.1063/1.2790432

Cited by 64 publications

(127 citation statements)

References 51 publications

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“…For D2 physisorbed on ASW ice the order of desorption is n = 1. If we take A = 10 13 s -1 and assume that it is independent of ν, Eν can be calculated for each TPD spectrum as follows: 28 Figure 3 displays the D2 coverage vs the desorption energy Eν on a 1-ML porous ASW film as calculated using Eq. (2).…”

Section: Dn/dt = R = -A ν N Exp(-eν/kt)mentioning

confidence: 99%

Changes in the morphology of interstellar ice analogues after hydrogen atom exposure

Accolla

Congiu

Dulieu

et al. 2011

Phys. Chem. Chem. Phys.

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The morphology of water ice in the interstellar medium is still an open question. Although accretion of gaseous water could not be the only possible origin of the observed icy mantles covering dust grains in cold molecular clouds, it is well known that water accreted from the gas phase on surfaces kept at 10 K forms ice films that exhibit a very high porosity. It is also known that in the dark clouds H2 formation occurs on the icy surface of dust grains and that part of the energy (4.48 eV) released when adsorbed atoms react to form H2 is deposited in the ice. The experimental study described in the present work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. Using the temperature-programmed desorption (TPD) technique and a method of inversion analysis of TPD spectra, we show that there is an exponential decrease in the porosity of the amorphous water ice sample following D-atom irradiation. This decrease is inversely proportional to the thickness of the ice and has a value of φ0 = 2 × 10 16 D-atoms cm -2 per layer of H2O. We also use a model which confirms that the binding sites on the porous ice are destroyed regardless of their energy depth, and that the reduction of the porosity corresponds in fact to a reduction of the effective area. This reduction appears to be compatible with the fraction of D 2 formation energy transferred to the porous ice network. Under interstellar conditions, this effect is likely to be efficient and, together with other compaction processes, provides a good argument to believe that interstellar ice is amorphous and non-porous. 1.IntroductionAmorphous solid water (ASW) is reputed to be the most abundant form of water in the Universe, thanks to its propensity for forming, molecule after molecule, as a deposit on interstellar dust particles. 1,2 The accretion of icy mantles (predominantly constituted by ASW) on silicate and carbonaceous dust grains takes place in interstellar molecular clouds. Some of them are cold (~10 K) and dense (10 4 -10 6 cm -3 ) regions where gaseous species heavier than hydrogen and helium freeze out onto the grains. Beside H2O and CO, other species constitute the inventory of icy mantles such as CO2, CH3OH, CH4, H2CO and NH3, 3,4 as a result of the gasgrain interactions occurring on the surface of interstellar dust. The most important and abundant molecular species as well, H2, is formed likewise thanks to reactions occurring on amorphous water ice in molecular clouds 5,6 . In addition, a significant fraction of the gas phase species is constituted by atomic hydrogen whose abundance is mostly governed by the destruction of H2 due to cosmic rays. It has been evaluated that, in dense clouds, the average number density ratio of atomic hydrogen component compared to the molecular one is ~ 0.1%. 7 In a dark cloud, atomic hydrogen thus represents the third most abundant gas-phase species, after H2 and He.Along with atoms and molecules available in the gas-phase and the condensed/adsorbed speci...

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Section: Dn/dt = R = -A ν N Exp(-eν/kt)mentioning

confidence: 99%

Changes in the morphology of interstellar ice analogues after hydrogen atom exposure

Accolla

Congiu

Dulieu

et al. 2011

Phys. Chem. Chem. Phys.

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“…CO on MgO(100) (Dohnálek et al 2001), D2 on amorphous solid water (Hornekaer et al 2005;Amiaud et al 2007), N2 on amorphous solid water (Zubkov et al 2007), benzene (C6H6) on amorphous silica (Thrower et al 2009) and NH3 on vapour deposited amorphous silicate (He et al 2015).…”

Section: Desorption Energy Determinationmentioning

confidence: 99%

“…For inclusion in kinetic simulations the E des (Θ) curve for Θi = 1 ML was described by a first order exponential fit which gives the full coverage dependence of the desorption energy in the sub-ML regime, as shown in Figures 6 (a) and (b). The corresponding distribution of desorption energies P (E des ) was then obtained from this fit using the following expression (Zubkov et al 2007):…”

Section: Desorption Energy Determinationmentioning

confidence: 99%

Thermal desorption of ammonia from crystalline forsterite surfaces

Suhasaria¹,

Thrower²,

Zacharias³

2015

Mon. Not. R. Astron. Soc.

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The thermal desorption of ammonia (NH 3 ) from single crystal forsterite (010) has been investigated using temperature-programmed desorption. The effect of defects on the desorption process has been probed by the use of a rough cut forsterite surface prepared from the cleaved forsterite sample. Several approaches have been used to extract the desorption energy and pre-exponential factor describing the desorption kinetics. In the sub-monolayer coverage regime, the NH 3 desorption shows a broad distribution of desorption energies, indicating the presence of different adsorption sites, which results in an apparent coverage-dependent desorption energy. This distribution is sensitive to the surface roughness with the cut forsterite surface displaying a significantly broader distribution of desorption energies compared to the cleaved forsterite surface. The cut forsterite surface exhibits sites with desorption energies up to 62.5 kJ mol −1 in comparison to a desorption energy of up to 58.0 kJ mol −1 for the cleaved surface. Multilayer desorption is independent of the nature of the forsterite surface used, with a desorption energy of (25.8±0.9) kJ mol −1 . On astrophysically relevant heating timescales, the presence of a coverage dependent desorption energy distribution results in a lengthening of the NH 3 desorption time-scale by 5.9 × 10 4 yr compared to that expected for a single desorption energy. In addition, the presence of a larger number of high-energy adsorption sites on the rougher cut forsterite surface leads to a further lengthening of ca. 7000 yr.

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“…In the present letter, we use ASW films sandwiched between decane layers to inhibit interface nucleation and to observe bulk ASW crystallization kinetics that are the result of bulk nucleation. The experiments were performed in an ultra-high vacuum system (UHV) that has been described in detail previously, 20,37 and only a high level description of the experiment is provided here. Briefly, the UHV chamber has a base pressure of <10 −10 Torr and the water films were deposited on a graphenecovered 1 cm diameter Pt(111) substrate.…”

mentioning

confidence: 99%

Communication: Distinguishing between bulk and interface-enhanced crystallization in nanoscale films of amorphous solid water

Yuan

Smith

Kay

2017

The Journal of Chemical Physics

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Adsorption, desorption, and diffusion of nitrogen in a model nanoporous material. I. Surface limited desorption kinetics in amorphous solid water

Cited by 64 publications

References 51 publications

Changes in the morphology of interstellar ice analogues after hydrogen atom exposure

Changes in the morphology of interstellar ice analogues after hydrogen atom exposure

Thermal desorption of ammonia from crystalline forsterite surfaces

Communication: Distinguishing between bulk and interface-enhanced crystallization in nanoscale films of amorphous solid water

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