Observation of exceptionally high vibrational excitation of hydrogen molecules formed by wall recombination.

Abstract

Relative densities of H atoms and ${\mathrm{H}}_{2}({v}^{\ensuremath{'}\ensuremath{'}})$ molecules in vibrational levels up to ${v}^{\ensuremath{'}\ensuremath{'}}=5$, effusing from a metal box containing heated tungsten filaments, were detected by a resonance-enhanced multiphoton ionization technique. The atom production is compatible with dissociation of molecules at the filament. The formation of ${\mathrm{H}}_{2}({v}^{\ensuremath{'}\ensuremath{'}})$ is attributed to an Eley-Rideal-type reaction, in which a free atom recombines with an adsorbed atom at the cold wall, followed by desorption. Above 2800 K we observe an abrupt drop in the atom and the ${\mathrm{H}}_{2}({v}^{\ensuremath{'}\ensuremath{'}})$ densities. It is ascribed to the effects of annealing on the filament surface.