Theory of Molecule-Surface Scattering at Thermal and Hyperthermal Energies

Iftimia, Ileana; Manson, J. R.

doi:10.1103/physrevlett.87.093201

Cited by 24 publications

(11 citation statements)

References 14 publications

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“…Thus an appropriate conclusion to draw from this work is that a scattering theory that accounts for the correct momentum conservation laws at a smooth surface gives better agreement with the measurements, the description still cannot be termed satisfactory. More recent calculations, for a non-rigid molecule that includes the possibility of excitation of internal molecular modes of vibration, agree nearly quantitatively with the measurements and shows that internal mode excitation is also very important in the scattering process [10].…”

supporting

confidence: 58%

Classical theory for scattering of rigid molecules from surfaces

Dai

Manson

2002

Nuclear Instruments and Methods in Physics Research Section B:

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A theoretical model is presented for the scattering of molecules from surfaces under conditions in which the major modes of energy transfer are multiple phonon excitation at the surface and rotational excitations of the molecule. Beginning from a completely quantum mechanical formalism, the classical limit is obtained for large mass molecules and large energies and in this limit the result is a closed-form expression for the scattering intensities. Results of calculations are compared with recent measurements for the scattering of hyperthermal beams of C 2 H 2 from a LiF(0 0 1) surface. The results of these comparisons indicate that a classical theoretical treatment of translational and rotational motion is adequate for describing this system. Ó 2002 Elsevier Science B.V. All rights reserved.In this paper a theoretical model is developed for the scattering of rigid molecules from surfaces where the modes of energy exchange are multiphonon excitation of the surface and rotational excitation of the molecule and both are treated in the classical mechanical limit. Classical mechanics has been shown adequate to explain the scattering of heavier atoms from surfaces [1,2] where large numbers of phonon transfers is the means of energy exchange. Classical mechanics even gives good descriptions of the energy transfer for the surface collisions of small mass projectiles such as He and D 2 at incident energies over 100 meV [3]. For molecules with masses substantially larger than hydrogen or deuterium, such as CO, CO 2 or C 2 H 2 , rotational quantum numbers even at temperatures as low as 100 K are of order 10 or larger and in a typical surface collision the rotational excitation can involve quantum numbers even larger than that. Thus for such molecules, a classical treatment of the rotational excitations, combined with a classical treatment of the phonon exchange should be adequate.An earlier treatment of this same problem has been presented based on treating the rotational interactions of a molecular beam incident on the surface as interactions with a surface of discrete scattering centers [4]. This earlier treatment obtained very good agreement with recent measurements of the angular distributions of C 2 H 2 [5] scattering from a LiF(0 0 1) surface at incident energies above 100 meV. Qualitative agreement was obtained with further experimental measurements of the scattered intensities as a function of final rotational energies. The work described here extends this earlier theoretical model to include a better model of the surface interaction, one in which the rotational interaction is with a surface having a smoothly varying repulsive barrier. In this case, the correct conservation of angular momentum perpendicular to the surface is included,

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supporting

confidence: 58%

Classical theory for scattering of rigid molecules from surfaces

Dai

Manson

2002

Nuclear Instruments and Methods in Physics Research Section B:

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“…10͒ are presented in another paper. 33 There it is shown that this theory can explain measured quantities, such as, angular distributions, scattered intensities as a function of the final rotational energy, and final rotational temperatures as functions of the incident beam energy. Thus it appears that the theoretical approach discussed here can be a useful tool in describing the surface scattering of certain classes of molecules.…”

Section: Discussionmentioning

confidence: 99%

Theory of mixed classical-quantum scattering of molecules from surfaces

Iftimia

Manson

2002

Phys. Rev. B

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A theoretical model is developed for describing the scattering of molecules from surfaces, which includes energy and momentum transfers between the surface and projectile for both translational and rotational motion, and internal-mode excitation of the projectile molecule. The translational and rotational motions, including multiphonon excitations with the surface, are treated in the classical limit. Internal-vibrational-mode excitation of the molecules is treated quantum mechanically, with extension to arbitrary numbers of internal modes and arbitrary excitation quantum numbers. Examples of calculations are carried out for the surface scattering of a simple diatomic molecule.

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“…Thermally-assistedtunneling model CH4 30 31 Manson 32 dependence of the angular intensity distribution from a corrugated surface. In the right-hand side, the distributions for e=1.0, 1.2 and 1.4 are shown divided by the initial orientation angle η .…”

Section: Ch4mentioning

confidence: 99%