Interaction of diatomic molecules with clean metal wire surfaces. Part 1.—Hydrogen on tungsten

Abstract

Heats of adsorption, sticking probabilities and temperature programmed desorption spectra are reported for hydrogen on polycrystalline tungsten at 88 and 290 K. The heats were measured using a fine-wire calorimeter, as invented by J. K. Roberts, but with automatic recording. The initial heat of adsorption onto a clean surface at 290 K was 192 ± 8 kJ mol^–1. Three desorption peaks were observed in the range 290–700 K. A discussion of the results is presented in terms of the crystal planes believed to be present at this polycrystalline surface. It is deduced that the heat of adsorption for hydrogen onto the (100) and (110) planes is 137 ± 5 kJ mol^–1 and that on these planes there is a repulsive interaction energy between near neighbours of 5.25 ± 0.50 kJ (mol pair)^–1. The importance of adatom interaction in this system is emphasised.