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.
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