| 1. |
- Romero Lejonthun, Liza, 1973, et al.
(författare)
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Chlorine interactions with water ice studied by molecular beam techniques.
- 2006
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Ingår i: The journal of physical chemistry. B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:46, s. 23497-501
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of chlorine interactions with ice at temperatures between 103 and 165 K have been studied using molecular beam techniques. The Cl(2) trapping probability is found to be unity at thermal incident energies, and trapping is followed by rapid desorption. The residence time on the surface is less than 25 microg at temperatures above 135 K and approaches 1 s around 100 K. Rate constants for desorption are determined for temperatures below 135 K. The desorption kinetics follow the Arrhenius equation, and activation energies of 0.24 +/- 0.03 and 0.31 +/- 0.01 eV, with corresponding preexponential factors of 10(12.08+/-1.19) and 10(16.52+/-0.38) s(-1), are determined. At least two different Cl(2) binding sites are concluded to exist on the ice surface. The observed activation energies are likely to be the Cl(2)-ice binding energies for these states, and the Cl(2)-surface interactions are concluded to be stronger than earlier theoretical estimates. The surface coverage of Cl(2) on ice under stratospheric conditions is estimated to be negligible, in agreement with earlier work.
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| 2. |
- Romero Lejonthun, Liza, 1973, et al.
(författare)
-
Formation of Adsorbed Layers by Deposition of Dinitrogen Pentoxide, Nitric Acid, and Water on Graphite
- 2009
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Ingår i: J. Phys. Chem. C. - : American Chemical Society (ACS). ; 113, s. 7728-7734
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Tidskriftsartikel (refereegranskat)abstract
- The formation of adsorbed layers of dinitrogen pentoxide, nitric acid, and water on graphite has been studied by molecular beam and light-scattering techniques. The desorption kinetics of N2O5 on graphite were described by the Arrhenius equation with an activation energy of 0.24 ± 0.03 eV and a pre-exponential factor of 2.3 × 10(10 ± 0.73) s−1, and N2O5 is concluded to bind more strongly than H2O to the graphite surface. Elastic helium scattering and light scattering were used to probe the formation of adlayers on the surface. Adsorption of pure N2O5 resulted in formation of thin adlayers at temperatures below 160 K. In coadsorption experiments N2O5 was concluded to facilitate the formation of thick N2O5−H2O ice layers at 155 K. In a similar way coadsorption of HNO3 and H2O resulted in the formation of thick adlayers at 170 K. N2O5 and HNO3 both bind more strongly than water to the graphite surface and are concluded to facilitate nucleation and growth of ice.
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| 3. |
- Romero Lejonthun, Liza, 1973, et al.
(författare)
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Interactions of N2O5 and Related Nitrogen Oxides with Ice Surfaces: Desorption Kinetics and Collision Dynamics
- 2014
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:47, s. 13427-13434
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Tidskriftsartikel (refereegranskat)abstract
- The detailed interactions of nitrogen oxides with ice are of fundamental interest and relevance for chemistry in cold regions of the atmosphere. Here, the interactions of NO, NO2, N2O4, and N2O5 with ice surfaces at temperatures between 93 and 180 K are investigated with molecular beam techniques. Surface collisions are observed to result in efficient transfer of kinetic energy and trapping of molecules on the ice surfaces. NO and NO2 rapidly desorb from pure ice with upper bounds for the surface binding energies of 0.16 +/- 0.02 and 0.26 +/- 0.03 eV, respectively. Above 150 K, N2O4 desorption follows first-order kinetics and is well described by the Arrhenius parameters E-a = 0.39 +/- 0.04 eV and A = 10((15.41.2)) s(1), while a stable N2O4 adlayer is formed at lower temperatures. A fraction of incoming N2O5 reacts to form HNO3 on the ice surface. The N2O5 desorption rates are substantially lower on pure water ice (Arrhenius parameters: Ea = 0.36 +/- 0.02 eV; A = 10(15.3 +/- 0.7) s(-1)) than on HNO3-covered ice (Ea = 0.24 +/- 0.02 eV; A = 10(11.5 +/- 0.7) s(-1)). The N2O5 desorption kinetics also sensitively depend on the sub-monolayer coverage of HNO3, with a minimum in N2O5 desorption rate at a low but finite coverage of HNO3. The studies show that none of the systems with resolvable desorption kinetics undergo ordinary desorption from ice, and instead desorption likely involves two or more surface states, with additional complexity added by coadsorbed molecules.
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| 4. |
- Romero Lejonthun, Liza, 1973
(författare)
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Molecular Beam Studies of Interactions Between Ice Surfaces and Atmospherically Relevant Molecules
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The discovery of the ozone hole over Antarctica in 1985 was one of the environmental issues that attracted most attention worldwide in the end of the last century. The cause of the ozone hole formation was proven to be coupled to the emission of chlorofluorocarbons (CFCs). The impact of the CFCs on the stratospheric chemistry was proven to be strikingly high. Eventually, research of heterogeneous chemistry showed the importance of the multi-phase reactions on stratospheric chemistry. The present thesis aims to contribute to the understanding of the heterogeneous processes relevant for stratospheric chemistry. The present thesis presents results from experimental studies of molecular beam interactions with surfaces, mainly water ice and graphite. Besides this, formation of adlayers of N2O5 and HNO3 on graphite surfaces has been studied by the use of helium scattering. Our results show that the interactions of both molecular chlorine and nitrogen oxides with the studied surfaces are highly inelastic in nature. At low incident energies (below about 0.15 eV), trapping desorption dominates completely and only at the highest energies employed, inelastic scattering is also present. Elastic scattering was not observed in any case. Furthermore, the results in this work show that the pre-exponential factor may deviate significantly from the common value of 1013 s-1 previously observed. The obtained pre-exponential factors ranged from about 1010 to 1016 s-1. This indicates that several of the studied desorption processes are complicated. The obtained activation energies were low in comparison to chemisorption energies, and were in the range of < 0.19-0.41 eV.
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