HIGHLY EXCITED HYDROGEN MOLECULES DESORBED FROM A SURFACE - EXPERIMENTAL RESULTS

The rovibrational excitation of hydrogen molecules resulting from reco mbination of atoms on a metallic surface has been observed by means of an electronic collision method. We present the obtained H- experiment al spectra reflecting the vibrational populations of the desorbed hydr ogen molecules. This study brings to light the fundamental role of the nature of the metallic surface in the recombination process: excitati on of higher vibrational levels (from v=5 to v=8) is observed only on those metal surfaces which strongly chemisorb atomic hydrogen. To expl ain these observations we propose the formation, on these surfaces, of a physisorbed H layer on the chemisorbed one.