Translational energy release in the recombinative desorption of H-2 from Ag(111)

We have investigated the recombinative desorption of H-2 from Ag(111) using (2+1) REMPI to detect the desorbing molecules. We describe a method for determining the energy released into translational motion normal to the surface over a wide range of surface temperatures. This was achieved by using a weak electric field to disperse the ions, in contrast to the usual field-free method. Calibration and analysis methods are discussed and energy distributions P(E) are reported for H-2 (v=0). Desorption from a 295 K surface shows only a single low-energy peak ((E) over bar=125 meV), whereas the translational energy release is bimodal for desorption from a 580 K surface, with mean desorption energies of approximately 140 meV and 1 eV for the two pathways. Sticking functions are calculated using detailed balance, revealing a large dependence on surface temperature. (C) 1997 Elsevier Science B.V.