Resonant charge transfer in the scattering of hydrogen atoms from a metal surface

Electron transfer and the production of negative hydrogen ions in the reflection of hydrogen atoms from a metal surface is studied theoretically. Starting from the total Hamiltonian of the metal--atom system, the time development of the one-electron density matrix is determined. This is shown to be related to the time-dependent coupling of the affinity level of the moving atom with the metal states. In the limit of weak coupling, the occupation probability of the affinity level can be obtained in a closed form. This theory is applied to the problem of negative hydrogen ion production at a W(110) surface, both with and without Cs coverage, and the results are compared with available experimental data and predictions of existing theories