Energy disposal via electron-hole pair excitation in atom recombination on metal surfaces: Electron distribution function and detailed balancing

The energy disposal via electron-hole (e-h) pair formation in the highly exoergic recombination of gas atoms on metal surfaces, has been studied. The impact of this excitation process on the energy spectrum of the metal electrons has been investigated at steady state. The energy distribution function of the electrons is shown to be non-thermal to an extent that depends on the reaction rate, probability distribution function for e-h pair creation and physical parameters of the material. The model has been applied to compute the electron spectra of metal surfaces, using kinetic data on H atom recombination that are available from the literature. The number of electrons made available for detection as chemicurrent has been derived and compared to experimental data on the H/Cu system. The interplay between the electron distribution function and the reaction kinetics is analysed by means of the principle of detailed balance. The detailed balancing analysis shows that, depending on the e-h excitation energy, the rate constant of energy transfer from the bath to the adlayer can be orders of magnitude larger than that proper for equilibrium conditions. (c) 2007 Elsevier B.V. All rights reserved.