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The adsorption of oxygen on a polycrystalline tungsten surface at ~300 K has been studied by means of electron stimulated desorption (ESD) Although precision gas dosing was not employed, the initial sticking probability for dissociative adsorption appears to be essentially unity, while the variation with coverage suggests that a high degree of order exists and that precursor state kinetics are significant. A most noticeable and reproducible discontinuity in ESD parameters occurs at a fractional coverage θ ~ 0.8 (exposure ~ 1.4 × 1015moleculescm2 incident) which is interpreted as an order-disorder transition within a single (β1) chemisorption state, and results in an increase in the ionic desorption cross-section by a factor of ~ 1.26. A discussion of the adsorption kinetics and the disorder transition is given in terms of current models of dissociative adsorption which include the effects of nearest neighbour lateral interactions.

Mass spectra produced by electron bombardment of H 2 , H 2 O and NH 3 solids are interpreted in terms of clustering about an energetic proton fragment. A self-consistent microphysical model is discussed, which permits the deduction of relevant lattice energy contributions and fragmentation energies.