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  • 1
    Electronic Resource
    Electronic Resource
    Surface scattering of NO from graphite: A statistical description of energy distributions (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 845-853 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the present theoretical study, inelastic scattering of NO from graphite surfaces is analyzed with a statistical model. The results are in good agreement with previous classical trajectory calculations by Pettersson et al. (1988). Angular distributions and the "rotational cooling'' effect found in experiments published by Frenckel et al. (1982), Segner et al. (1983), and Häger and Walther (1984) are successfully reproduced. The model describes a small part of the graphite surface together with a scattering diatom as a collision complex, which decomposes in a unimolecular fashion. The surface is assumed to be flat, whereby the diatom angular momentum component along the surface normal and the linear momentum parallel to the surface are conserved. Otherwise the diatom translation and rotation are allowed to exchange energy with the surface, which is characterized by a set of harmonic oscillators. The experimentally observed "rotational cooling'' effect is clearly demonstrated to be due to the conservation of the normal component of the angular momentum. The surface oscillator mass and the number of surface oscillators are treated as parameters. The results indicate that on the average one to three surface atoms are directly involved in each molecule-surface collision. "Rotational rainbow''-like distributions are observed at high total energies, even though the simulations are purely statistical with no dynamic effect included.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459454
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  • 2
    Electronic Resource
    Electronic Resource
    A classical trajectory study of inelastic scattering of NO from graphite surfaces: Rotational energy distributions (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6963-6971 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The inelastic scattering of NO molecules from graphite surfaces is studied by classical trajectory methods. The experimental results from Frenkel et al. (1982), Segner et al. (1983), and Häger and Walther (1984) are analyzed. A model using a small isolated part of the graphite surface in interaction with the NO molecule gives results in good agreement with experiment. The parameter values in the model are fixed at the values previously found to reproduce the angular distributions well [Nyman and Pettersson (1987)]. For this system, the experimental results give a "rotational cooling'' such that the rotational temperature of the inelastically scattered molecules becomes smaller than the surface temperature. This effect is reproduced accurately by the calculations, giving a rotational temperature of 250 K, independent of the surface temperature above 300 K. The main factor controlling this inelastic rotational cooling is the low initial value of the normal component of the total angular momentum. A "rotational rainbow'' structure is found in the calculations in many cases, primarily at high surface temperatures. The final energy distributions are shown to be mainly statistical by application of a unimolecular decomposition picture, similar to the common RRK type model used for gas phase reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455322
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  • 3
    Electronic Resource
    Electronic Resource
    A Monte Carlo trajectory study of angular distributions in inelastic scattering of NO from graphite surfaces (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5825-5829 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A Monte Carlo classical trajectory study of NO/graphite surface scattering was carried out. NO was modeled as a rigid rotor interacting with a smooth vibrating surface through two Lennard-Jones 12-6 potential terms. The study simulated the experiments performed on the same system, first published by Frenckel et al. (1982). Angular distributions were calculated and found to generally reproduce the measured scattering lobes best at a simulated surface mass of 18 amu. Two potential well depths were used and at the larger of these all measured lobes could be quite well reproduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452512
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  • 4
    Electronic Resource
    Electronic Resource
    Collision complex model of molecules scattering from corrugated surfaces (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 4239-4250 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A collision complex that gives almost quantitative agreement with a large set of data for inelastic scattering of atoms and molecules from surfaces is presented. In the model, a scattering molecule and a small part of the surface form a collision complex, that decomposes in a unimolecular fashion after statistical redistribution of energy. Both molecular translation and rotation are included in the model, and the surface is represented by a small number of harmonic oscillators. The surface is considered as locally flat at the place of impact, and surface corrugation is represented by a Gaussian distribution of local normal directions. Analytical solutions of simple integrals clearly illustrate the functional dependence on the principal parameters: translational energy, scattering angle, surface temperature, the relative size of the surface directly interacting with a scattering molecule, and the active degrees of freedom. Angular distributions for atoms, diatomic and polyatomic molecules scattering from metals, graphite and liquid surfaces are shown to be in good agreement with experimental results at thermal translational energies, and at least up to 0.5 eV. The model provides a simple and useful way to interpret and inter-relate experimental results, and makes it possible to evaluate the total information content in experimental data. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469471
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  • 5
    Electronic Resource
    Electronic Resource
    Evaporation model of cluster scattering from surfaces (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 3911-3924 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present classical trajectory calculations of ArnNem (n+m=111, 859) clusters scattering from a rigid surface. The dynamics of energy transfer and cluster decomposition during surface scattering is investigated for incident velocities of 100–700 m/s. The initial translational energy is at impact effectively transferred into internal degrees of freedom of the cluster. The overall energy transfer efficiency is very high but not complete, leaving too much energy in translation. No fragmentation takes place below 200 m/s. At incident velocities below 450 m/s, evaporation of small fragments from the heated cluster takes place in thermal equilibrium with the vibrational degrees of the cluster. This thermal evaporation is also the dominating ejection channel up to 700 m/s. Above 450 m/s, the formation of a compressed zone at impact opens up a new channel with ejection of fast fragments parallel to the surface plane. This effect becomes increasingly important at higher velocities. An evaporation model where fragmentation of the heated cluster takes place as isotropic and thermal ejection of small fragments is concluded to account for the major fragmentation processes observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466326
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  • 6
    Electronic Resource
    Electronic Resource
    Ozone photodissociation in the Hartley band: A statistical description of the ground state decomposition channel O2(X 3Σ−g)+O(3P) (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8887-8896 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ozone photodissociation in the Hartley band O3+hν→O(3P)+O2(X 3Σ−g) is simulated with a statistical model. In the model, energy is partitioned at a decoupling distance which is located at a position with nonzero potential energy on a repulsive and dissociative potential energy surface. Introduction of the repulsive potential on which dissociation takes place, and the choice of decoupling distance is shown to be of crucial importance for the final energy distributions, and in particular it determines the amount of energy left in translation. The model is shown to give good agreement with experimental vibrational and translational energy distributions, while the rotational distributions predicted by the model seem less peaked than experimental data. Vibrational state distributions are calculated for different dissociation wavelengths in the Hartley band (200–310 nm), and they are concluded to deviate substantially from distributions previously used in atmospheric modeling. The statistical approach is compared to impulsive and statistical models, and also related to recent quantum mechanical calculations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468942
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  • 7
    Electronic Resource
    Electronic Resource
    Surface scattering of NO from Ag[111]: A statistical description of rotational energy distributions (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 2359-2365 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A statistical model is applied to inelastic scattering of NO molecules from the Ag[111] surface. Calculated final rotational energy distributions are found to be in good agreement with experimental distributions including pronounced "rotational rainbows'' [Phys. Rev. Lett. 47, 1169 (1981)]. The model has previously been applied to NO scattering from graphite at lower collision energies [J. Chem. Phys. 93, 845 (1990)]. In the model, a scattering molecule and a small part of the surface form a collision complex which decomposes in a unimolecular fashion. The molecule is treated as a rigid rotor, and the simulated part of the surface as a few harmonic oscillators. The calculations indicate that the experimental results to a first approximation are statistical, and that no detailed dynamics have to be taken into consideration to explain them. The shape of the rotational energy distributions is due to conservation of the angular momentum component in the surface normal direction, introduced since the surface is treated as flat. Rotational rainbows are thus reproduced without introducing any detailed information about the molecule–surface interaction potential. The number of surface oscillators used in the model is varied, and in general one to four oscillators best reproduce the experimental results. The calculations indicate that the angular acceptance of the laser-induced fluorescence experiments is of large importance for the obtained final rotational energy distributions. An analytical solution to the statistical problem is derived for the case of fixed initial energy terms, and it is shown to describe well the experimental distributions here discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466482
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  • 8
    Electronic Resource
    Electronic Resource
    Classical trajectory study of argon–ice collision dynamics (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 5380-5391 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Classical trajectory simulations have been used to study Ar–ice Ih collisional energy transfer, trapping coefficients and scattering distributions for initial Ar kinetic energies between 0.1 and 2.0 eV, incident angles between 0 and 70° and surface temperatures between 0 and 300 K. Collisional energy transfer is extremely efficient due to substantial transfer of energy from the Ar atom to the ice surface over typically 2–4 gas-surface encounters, and the rapid dissipation of this energy away from the collision center, preventing energy transfer back to the Ar atom. This leads to large trapping coefficients over this range of Ar collision energies, incident angles and surface temperatures. Scattered gas atoms lose most of their initial kinetic energy and have broad angular distributions. The large trapping coefficients obtained for the Ar–ice collisions are expected to be found for similar reactions under stratospheric conditions (e.g., HCl–ice, HOCl–ice and ClONO2–ice). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478433
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  • 9
    Electronic Resource
    Electronic Resource
    Scattering and trapping dynamics of gas-surface interactions: Theory and experiments for the Xe-graphite system (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 10339-10349 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on molecular beam experiments and molecular dynamics simulations of xenon scattering with incident energies E=0.06−5.65 eV from graphite. The corrugation felt by an atom interacting with the surface is found to be influenced by both surface temperature, Ts, and E. Angular distributions are significantly broadened when Ts is increased, clearly indicating corrugation induced by thermal motion of the surface also at the highest E employed. Direct scattering dominates for high E, while trapping becomes important for kinetic energies below 1 eV. The coupling between atom translation and surface modes in the normal direction is very effective, while trapped atoms only slowly accommodate their momentum parallel to the surface plane. The very different coupling normal and parallel to the surface plane makes transient (incomplete) trapping-desorption unusually pronounced for the Xe/graphite system, and atoms may travel up to 50 nm on the surface before desorption takes place. The nonlocal and soft character of the Xe-graphite interaction compared to interactions with close packed metal surfaces explains the observed high trapping probabilities and the lack of structural corrugation effects at high kinetic energies. Experimental results and simulations are in good agreement for a wide range of initial conditions, and we conclude that the model contains the most essential features of the scattering system. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477689
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  • 10
    Electronic Resource
    Electronic Resource
    Scattering and trapping dynamics of gas-surface interactions: Vibrational excitation of CF3Br on graphite (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 10350-10360 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results from molecular beam experiments and classical trajectory calculations of CF3Br scattering from graphite. Direct inelastic scattering dominates for initial translational energies Etr=0.6–3.5 eV and surface temperatures Ts=500–1170 K. An increase in the CF3Br vibrational temperature is observed in the scattered flux using the method of electron impact-induced fragmentation. The vibrational excitation depends on Etr and Ts, and a maximum vibrational temperature increase of 254±15 K is reached for Etr=3.5 eV and Ts=830 K. The vibrational excitation, angular distributions, and average translational energies are semi-quantitatively reproduced by classical trajectory calculations, indicating that the vibrational excitation can be explained by an electronically adiabatic "mechanical" process. The calculations suggest that a large fraction of the incident molecules experience multiple collisions with the surface. These transiently trapped molecules are slowly vibrationally excited while moving long distances, and are not thermalized even after 100 ps on the surface. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477690
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