Dynamics of the formation of CD₄ from the direct reaction of incident D atoms with CD₃/Cu(111)

Abstract

Using molecular beam techniques we find that incident D atoms can abstract CD3 from a Cu(111) surface to yield CD4 in a direct (Eley-Rideal) gas-surface reaction with a cross section of ∼10-16 cm2/D atom. Dynamical evidence for a direct reaction includes the observation of an extremely sharp angular distribution that is clearly displaced from the surface normal, and the determination of a very high translational energy of the product, Ef, which is ∼2 eV. For a 0.25 eV D-atom beam incident at 45° on a 95 K surface, this energy varies with the detection angle, θf, as Ef(θf) = (1.8+θf/45) eV, where θf0° in the "backscattering'' direction. For these conditions, the angular distribution approximately follows the function cos70(θf-5.5), being peaked 5.5° from the normal with a full width at half maximum of <17°. Lowering the beam energy to 0.07 eV gives a broader angular distribution peaked at about 1.5° from the normal, consistent with cos60(θf-1.5). The reaction with 0.25 eV H incident at 45° gives a similar distribution peaked at ∼3.5° from the normal. The shifts in the angular distributions are approximately consistent with parallel momentum conservation. The CD3/Cu(111) surface was prepared by thermal dissociation of CD3I on the surface or by adsorbing CD3 directly from a CD3 beam produced by the pyrolvsis of azomethane. © 1996 American Institute of Physics.