Time-of-flight studies on desorbing and on scattered D-2 molecules from a V(111)+S surface

Using a time-of-flight spectrometer we have measured the translational ener gy distribution of deuterium molecules originating from a sulfur-covered va nadium(1 1 1) surface. We have studied the energy accommodation coefficient (EAC of D-2 after scattering of a room temperature D-2 gas on the surface. An EAC of 0.37, independent of the surface temperature, is obtained. Furth ermore, we have investigated the mean translational energy of D-2 molecules desorbing isothermally from the surface at 950 K. A hyperthermal desorptio n flux has been observed, corresponding roughly to a Maxwellian of 3200 K. From these results we conclude that the potential energy surface for the D- 2-V(1 1 1) + S system is characterized by an activation barrier for dissoci ative adsorption of about 0.22 eV and a non-existing physisorption well in front of the barrier. (C) 2001 Elsevier Science B.V. All rights reserved.