Recombination of H atoms on glass and silica

Many more measurements have been made of the recombination efficiencies of glass and silica than of any other materials, for the simple reason that most apparatuses are made of either glass or silica and the wall recombination efficiency is a natural by-product of most investigations. The recombination is predominantly first order and the more systematic measurements, for these recombination kinetics, are shown in Fig. 24 presently, we will see that, under some conditions, the recombination can be second order. Up to a threefold scatter in the values of 7 have been found even for the one apparatus (Melin and Madix [90]) depending on the history of the glass, but Fig. 24 demonstrates that there are also substantial systematic differences between the results obtained by different workers. 

Wood and Wise [91] reported that at sufficiently high and sufficiently low temperatures, the recombination of H atoms on Pyrex and quartz becomes second order (see Fig. 25). Their experimental values of 7 were always calculated on the assumption of pure first-order or pure second-order kinetics, whereas, in fact, intermediate orders prevail in the quite broad transition regions. The values of 7 obtained for the high temperatures (T 500 K) do not appear to be much affected by this simplification, 

Percentage contribution to the overall rate of recombination of component 

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