Interaction of microwave discharge-produced atomic hydrogen with Ru(001)

We have investigated the reaction of gas-phase atomic hydrogen (deuterium) with deuterium (hydrogen) precovered Ru(001) surfaces. The microwave discha rge atomic hydrogen source utilized in the present work produced results di ffering from those obtained in previous investigations with a hot filament source. Whereas exposure to the hot filament source resulted in a saturatio n coverage of theta(H) = 1.42 +/- 0.03, exposure to the microwave discharge results in a coverage of only theta(H) = 1.01 +/- 0.02. We have observed a n isotope effect in the removal of adsorbed H (D) by exposure to gas-phase atomic D (H) at 100 K, namely, H(a) is replaced more readily by D(g) (cross section of sigma(r) = 8.9 +/- 0.3 x 10(-17) cm(2)) than is D(a) by H(g) at this temperature (sigma(r) = 4.7 +/- 0.3 x 10(-17) cm(2)). We also report an isotope effect in the surface temperature dependence of the abstraction cross section. The cross section for the abstraction of D(a) by H(g) shows a greater increase with increasing surface temperature (activation energy o f E-a = 266 +/- 28 cal/mol) than does the cross section for the abstraction of H(a) by D(g) (E-a = 65 +/- 12 cal/mol). (C) 1999 Elsevier Science B.V. All rights reserved.