| Research Abstract |
In order to clarify the mechanism behind dynamical processes at solid surfaces such as dissociative adsorption and associative desorption of hydrogen, photo-stimulated desorption of adsorbed molecules, quantum transport phenomena, and transient response of surface electron system to ultrashort laser pulses, it is necessary to have an aocurate knowledge of potential energy surfaces, excited as well as the ground states of electron system, and the enterrelation between electronic transitions and state-changes of molecular motion. With this in mind, theoretical studies on dynamical processes at solid surfaces have been done. The obtained results are summarized as follows.
1. Making stress on the spatial as well as temporal locality of electronic excitations, we have investigated trajectories of molecules in photo-stimulated desorption. On the basis of the obtained results, dependences of the desorption probability on energy, time duration, and penetration depth of laser pulses are clarifie
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2. As a dynamical quantum filter, the orientation dependent activation barrier can select rotational states of molecules which attempt to pass through the barrier and to desorb. On the way toward the vacuum from the barrier (transition region), molecules are rotationally excited, de-excited, or retain rotational states at the transition region. It is found that molecules rotationally de-excited as well as those retaining rotational states at the transition region do helicopter-like rotational motion, and that molecules rotationally excited do cartwheel-like rotational motion.
3. An expression of time-resolved two-photon photoemission spectrum is derived from a microscopic point of view. On the basis of the obtained results, it is clarified how the information about the lifetime of intermediate states at surfaces can be obtained by the cross correlation trace. Furthermore, the effects of inter-band excitations on the cross correlation trace are clarified.
4. The electron correlation effects on electron transport phenomena in an atom-sized contact between an STM-tip and a metal surface are investigated with the aid of the Hubbard Hamiltonian. It is shown that intra-and inter-subband scattering of traveling electrons are induced by Coulomb interacion at finite-temperatures and that the step wise variation of the conductance as a function of the stretching distance of the STM-tip is considerably affected. Less
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