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Theoretical studies of molecule surface scattering: Rotationally inelastic diffraction and dissociative dynamics of hydrogen on metals
Abstract
The interaction of H$\sb2$ and its isotopes with metal surfaces has been the subject of many experimental as well as theoretical investigations in the last years. The scattering experiments are capable of providing a wide range of data such as the final rotational state distribution, sticking coefficients, kinetic energy distribution, as well as diffraction data. The major progress that has occured in the experimental methods has provided a challenge to theory since there is a need for developing models for the interpretation and analysis of the measured data. At the same time the tremendous increase in computational power in recent years has made possible the implementation of detailed dynamics simulations of dissociative and diffractive molecular scattering. In the first study of this thesis we implemented a model for looking at the rotationally inelastic diffraction probabilities for H$\sb2$, HD, and D$\sb2$, as a function of surface temperature. In this model the surface is treated in a quantum mechanical fashion using a recently developed formalism. The center of mass translational motion is treated semiclassically using Gaussian wave packets, and the rotations are described quantum mechanically. The phonon summed rotation-diffraction probabilities as well as the probability distribution for a scattering molecule exchanging an amount of energy $\Delta$E with the surface were also computed. In the second and third study of this thesis we implemented a mixed quantum-classical model to compute the probability for dissociation and rotational excitation for H$\sb2$, HD, and D$\sb2$ scattered from Ni(100) and Cu(100) surfaces. In these studies we focus on the problem of dimensionality in dynamics simulations. Of the six degrees of freedom for the dissociative adsorption of a diatomic molecule on a static surface, we treat Z, the center of mass distance above the surface plane, r, the internuclear separation, and $\theta$, the polar orientation angle, quantum mechanically. The remaining three degrees of freedom, X and Y, the center of mass position on the surface plane, and $\phi$, the azimuthal orientation angle, are treated classically. Probabilities for dissociation and ro-vibrational excitation are computed as a function of incident translational energy. Two sudden approximations are tested, in which either the center of mass translation parallel to the surface or the azimuthal orientation of the molecule are frozen. Comparisons are made between low and high dimensionality results as well as with fully classical results.
Subject Area
Physical chemistry|Chemistry
Recommended Citation
Cruz Pol, Astrid J, "Theoretical studies of molecule surface scattering: Rotationally inelastic diffraction and dissociative dynamics of hydrogen on metals" (1993). Doctoral Dissertations Available from Proquest. AAI9316636.
https://scholarworks.umass.edu/dissertations/AAI9316636