QUANTUM DISSIPATIVE DYNAMICS OF ADSORBATES NEAR METAL-SURFACES - A SURROGATE HAMILTONIAN THEORY APPLIED TO HYDROGEN ON NICKEL

Dissipative dynamics of an adsorbate near a metal surface is formulate d consistently by replacing the infinite system-bath Hamiltonian by a finite surrogate Hamiltonian. This finite representation is designed t o generate the true short time dynamics of a primary system coupled to a bath. A detailed wave packet description is employed for the primar y system while the bath is represented by an array of two-level system s. The number of bath modes determines the period the surrogate Hamilt onian reproduces the dynamics of the primary system. The convergence o f this construction is studied for the dissipating Harmonic oscillator and the double-well tunneling problem. Converged results are obtained for a finite duration by a bath consisting of 4-11 modes. The formali sm is extended to dissipation caused by electron-hole-pair excitations . The stopping power for a slow moving proton is studied showing devia tions from the frictional limit at low velocities. Vibrational line sh apes of hydrogen and deuterium on nickel were studied. In the bulk the line shape is mostly influenced by nonadiabatic effects. The interpla y between two baths is studied for low temperature tunneling between t wo surface sites of hydrogen on nickel. A distinction between lattice modes that enhance the tunneling and ones that suppress it was found. (C) 1997 American Institute of Physics.