INTERACTION OF H2 WITH (100) .1. BINDING STATES

Flash desorption mass spectrometry is used to study the structures and kinetics of hydrogen adsorption on the (100) plane of tungsten. It is shown that there are two binding states, β1 and β2 in a saturation ratio of 2:1 which obey first- and second-order kinetics, respectively. The activation energies of desorption are 26.3 and 32.3 kcal mole-1 and both vary with coverage by less than 0.5 kcal monolayer-1. Deuterium isotope effects, exchange, and replacement are also examined. These results combined with recent LEED measurements for this system are used to formulate a structure for the adsorbate which appears to quantitatively explain the presently available data. This structure is shown to be reasonable on the basis of the electronic structure of the substrate which predicts multiple states, a c(2×2) structure, and island formation at low coverage as observed.