Optical second-harmonic generation is used as a sensitive, nondestructive probe for the thermally activated dissociation of molecular oxygen on Si(111)7×{}7. Isothermal measurements show that the dissociation kinetics strongly depend on the total oxygen coverage. At room temperature the 1/e lifetime of chemisorbed O₂ is {~}15 min for saturation coverage but {~}50 min for low oxygen coverage. The temperature dependence of the dissociation rates between 80 and 500 K indicates that more than one dissociation channel and/or molecular oxygen species exist on the surface.
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Bratu et al. (1994) studied this question.