COLLISION-INDUCED DESORPTION (CID) OF NO FROM PT(111) - A COMPARISON BETWEEN THE CID BINDING-ENERGY AND THE ACTIVATION-ENERGY FOR THERMAL-DESORPTION

The Xe and Kr collision-induced desorption cross-sections for NO adsor bed on Pt(111) at 100 K are reported as a function of translational en ergy in the range of 1.9 to 3.8 eV. The minimum energy required for de sorption is extracted using extrapolation to the zero of cross-section . The measured threshold energies exhibit total energy scaling for bot h beams using two angles of incidence, 45 degrees and 15 degrees. The threshold energies required to desorb NO from PI(111) were determined experimentally to be 2.55 eV and 2.05 eV using Xe or Kr respectively. Using a hard sphere/cube collision model the NO-Pt(111) binding energy was calculated to be 1.12 +/- 0.02 eV using either the beam of Xe or Kr. Comparison of this binding energy with the measured activation ene rgy for thermal desorption supports an adsorption/desorption model hav ing no precursor to the chemisorption state. (C) 1998 Published by Els evier Science B.V.