HYDROGEN-ATOM REACTIONS WITH MONOLAYER GRAPHITE EDGES ON PT(100) SURFACES - HYDROGENATION AND H ABSTRACTION

The interaction of thermal H(D) atoms with monolayers of graphite depo sited on Pt(100) surfaces was studied with LEED, AES, TDS and HREELS. H (D) atoms react with C atoms at the zigzag and armchair edges of C i slands via the formation of sp(3) CH(CD) and CH2(CD2) edge groups. The initial transformation C-->CH(CD) occurs with a constant probability via a precursor state which is restricted to the immediate vicinity of the edges. The hydrogenation of monohydride CH(CD) groups to dihydrid e CH2(CD2) occurs with a cross-section of about 1.5 Angstrom(2). The a bstraction reactions of H(D) from monohydride and dihydride groups by H or D vis H-2 (D-2) formation have cross-sections of 0.1 and 1 Angstr om(2), respectively. The magnitude of these cross-sections are expecte d for direct Eley-Rideal-type reactions. Isotope exchange reactions we re measured by subjecting dihydride CD2(CH2) groups to fluences of H ( D) atoms. The observed cross-sections suggest a direct exchange via HCD2-->CDH+D. (C) 1998 Elsevier Science B.V.