Highly excited hydrogen molecules desorbed from a surface: Experimental results

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