Time-of-flight studies on desorbing and on scattered D2 molecules from a V(1 1 1) + S surface

Using a time-of-flight spectrometer we have measured the translational energy distribution of deuterium molecules originating from a sulfur-covered vanadium(1 1 1) surface. We have studied the energy accommodation coefficient (EAC) of D2 after scattering of a room temperature D2 gas on the surface. An EAC of 0.37, independent of the surface temperature, is obtained. Furthermore, we have investigated the mean translational energy of D2 molecules desorbing isothermally from the surface at 950 K. A hyperthermal desorption flux has been observed, corresponding roughly to a Maxwellian of 3200 K. From these results we conclude that the potential energy surface for the D2–V(1 1 1) + S system is characterized by an activation barrier for dissociative adsorption of about 0.22 eV and a non-existing physisorption well in front of the barrier.