| 1. |
- Andersson, Patrik U, 1970, et al.
(författare)
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Water Condensation on Graphite Studied by Elastic Helium Scattering and Molecular Dynamics Simulations
- 2007
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:42, s. 15258-15266
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Tidskriftsartikel (refereegranskat)abstract
- Formation of water/ice layers on graphite has been studied in the temperature range from 90 to 180 K by elastic helium scattering, light scattering, and molecular dynamics simulations. Combined helium- and light-scattering experiments show that an ice film that wets the graphite surface is formed at surface temperatures of 100-140 K, whereas three-dimensional ice structures are formed at 140-180 K. Desorption of adsorbed water molecules competes with water incorporation into the ice film, and the ice formation rate is strongly temperature dependent. At 150 K, ice-layer formation takes place at the same time scale as layer reconstruction, and its properties are sensitive to the water deposition rate. The experimental results are compared with kinetics models, and the Johnston-Mehl-Avrami-Kolmogorov model is concluded to well describe the ice-layer formation kinetics in the whole temperature range. Molecular dynamics simulations of water-cluster formation on graphite at 90-180 K show that water molecules and small clusters are highly mobile on the surface, which rapidly results in the nucleation of large and less mobile clusters on the surface. Clusters formed at low temperature tend to have the most molecules in direct contact with the uppermost graphite layer, while multilayer cluster structures are preferred at high temperatures. The results are discussed and compared with earlier studies of water ice formation on solid surfaces.
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| 2. |
- Suter, Martina, 1966, et al.
(författare)
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Argon collisions with amorphous water ice surfaces
- 2006
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Ingår i: Chemical Physics. ; 326:2-3, s. 281-288
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of argon atom collisions with amorphous ice surfaces are investigated using molecular beam techniques and molecular dynamics simulations. The formation of an amorphous ice layer on top of crystalline ice at 110 K is shown to have a strong influence on Ar scattering. Compared to crystalline ice, trapping followed by desorption is favoured over inelastic scattering, and a strongly enhanced emission of argon in the backward direction is observed. Molecular dynamics simulation with different types of amorphous and crystalline surfaces are consistent with the experimental data and show that large scale corrugation is required to reproduce the experimental findings. It is concluded that argon scattering can be used to probe changes in surface structure on the nanometer length-scale, while it is relatively insensitive to changes on the molecular level, and it thereby complements other techniques for studies of structural changes of ice surfaces. (c) 2006 Elsevier B.V. All rights reserved.
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| 3. |
- Suter, Martina, 1966, et al.
(författare)
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Formation of water-ammonia ice on graphite studied by elastic helium scattering
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 445, s. 208-212
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Tidskriftsartikel (refereegranskat)abstract
- Helium and light scattering experiments have been performed to study the formation of water–ammonia ice layers on graphite at 110–160 K. Ice formation is mainly governed by the partial water pressure, but the presence of ammonia enhances the formation rate and influences the layer properties. Ice formed at temperatures <140 K wets the surface, while ice formed at higher temperatures does not. At temperatures around 140 K ammonia destabilizes the two-dimensional ice layers and a dewetting transition is observed at a surface coverage of 90–95%.
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| 4. |
- Suter, Martina, 1966, et al.
(författare)
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Molecular Beam studies of Carbon Monoxide Interactions with Water Ice.
- 2004
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Ingår i: Physica Scripta. ; T110:doi:10.1238/Physica.Topical.110a00350, s. 350-354
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of CO interactions with water ice surfaces are studied using molecular beam techniques. The experimental method allows for detailed investigations of interaction between molecules and ice surfaces under single collision conditions, and collision dynamics and energy transfer are characterized. An ice surface is prepared by deposition of water vapor on a cold substrate and the surface is maintained in a vacuum chamber with a partial water vapor pressure up to 10-4 mbar, which allows for experiments with ice surfaces in the temperature range 100–190 K. A molecular beam is directed towards the ice surface, and the molecular flux from the surface is detected by mass spectrometry. Angular-resolved intensity and time-of-flight distributions are measured, and the effects of surface temperature, incident translational energy and incident angle are investigated. The surface collisions are highly inelastic with large energy loss observed for the directly scattered flux, similar to the results for the previously studied Ar-ice and HCl-ice systems. The data for the energy loss as a function of scattering angle show that energy transfer is substantial both parallel and perpendicular to the surface plane. The trapping of CO on the surface is found to be very effective under typical thermal conditions. The molecules accommodate to the temperature of the ice, but rapidly leave the surface by desorption because of the low binding energy to the surface.
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| 5. |
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| 6. |
- Suter, Martina, 1966, et al.
(författare)
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Surface properties of water ice at 150-191 K studied by elastic helium scattering.
- 2006
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:17
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Tidskriftsartikel (refereegranskat)abstract
- A highly surface sensitive technique based on elastic scattering of low-energy helium atoms has been used to probe the conditions in the topmost molecular layer on ice in the temperature range of 150-191 K. The elastically scattered intensity decreased slowly as the temperature was increased to about 180 K, followed by a rapid decrease at higher temperatures. An effective surface Debye temperature of 185+/-10 K was calculated from the data below 180 K. The changes in the ice surface above 180 K are interpreted as the onset of an anomalous enhancement of the mean square vibrational amplitude for the surface molecules and/or the onset of a limited amount of disorder in the ice surface. The interpretation is consistent with earlier experimental studies and molecular dynamics simulations. The observed changes above 180 K can be considered as the first sign of increased mobility of water molecules in the ice surface, which ultimately leads to the formation of a quasiliquid layer at higher temperatures. A small shift and broadening of the specular peak was also observed in the range of 150-180 K and the effect is explained by the inherent corrugation of the crystalline ice surface. The peak shift became more pronounced with increasing temperature, which indicates that surface corrugation increases as the temperature approaches 180 K. The results have implications for the properties and surface chemistry of atmospheric ice particles, and may contribute to the understanding of solvent effects on the internal molecular motion of hydrated proteins and other organic structures such as DNA.
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