3180.     SHULER, K. E., AND LAIDLER, K. J.  Kinetics of Heterogeneous Atom and Radical Reactions.  I.  Recombination of Hydrogen Atoms on Surfaces.  Jour. Chem. Phys., vol. 17 1949, pp. 1212-1217; Chem. Abs., vol. 44, 1950, p. 4760.

        Data on the kinetics of the recombination of H atoms on various types of surfaces are analyzed in the light of the theory of absolute reaction rates.  Expressions are derived for the recombination coefficient and the 1^st-order-rate constant, enabling these quantities to be calculated on the basis of postulated mechanisms.  The experimental activation energies are consistent with estimates using either Hirschfelder’s rule or an expression utilizing the experimental desorption temperature.  For the reaction on dry oxides and dry glass, good agreement is found, assuming that reaction occurs between a gas-phase H atom and an adsorbed H atom, the adsorption being of the van der Waals type at low temperatures and chemisorption at higher ones.  The mechanism of surface poisoning by water vapor is not due to the necessity for desorbing the water molecule:  In the high-temperature region it is due to an increase in activation energy, the mechanism being S-OH+H→S-O+H₂; in the low-temperature region it is due to a decrease in the number of active centers, the reaction being between a gaseous atom and a van der Waals adsorbed H atom above the water layer.