Sticking probabilities of hydrogen on molybdenum films and filaments

Abstract

The variation of sticking probability s with surface coverage has been studied for the adsorption of hydrogen on molybdenum at 300, 195 and 78°K. Initial values of s at 300°K are 0.37 on filaments and ca. 0.68 on sintered films. s falls linearly with increase in surface coverage at 300°K, as required by the Langmuir model of the adsorption process in which molecules striking occupied sites are desorbed. A similar fall in s from 0.73 to 0.40 is observed during the initial stages of adsorption on sintered films at 78°K, although the operation of a precursor state is indicated at this temperature. Behaviour at 195°K is complicated by a limited surface mobility which enables equilibrium of the adsorbate to be achieved between inner and outer surfaces but not between one region of the film and another.