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 met hod for determining the energy released into translational motion norm al to the surface over a wide range of surface temperatures. This was achieved by using a weak electric held to disperse the ions, in contra st to the usual field-free method. Calibration and analysis methods ar e 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 bimo dal for desorption from a 580 K surface, with mean desorption energies of approximately 140 meV and 1 eV for the two pathways. Sticking func tions are calculated using detailed balance, revealing a large depende nce on surface temperature. (C) 1997 Elsevier Science B.V.