INTERACTION OF GASEOUS D ATOMS WITH CH3I ADSORBED ON PT(111), H PT(111), AND C/PT(111) SURFACES - FROM HOT-ATOM TO ELEY-RIDEAL PHENOMENOLOGY/

The interaction of gaseous D atoms with methyl iodide molecules adsorb ed on Pt(111), hydrogen saturated Pt(111), and graphite monolayer cove red Pt(111) surfaces was studied. Direct product rate measurements wer e employed to determine the reaction kinetics. On all substrates, inco ming D atoms abstract the methyl group from adsorbed CH3I via gaseous CH3D formation. in the monolayer regime of CH3I/Pt(111) pure hot-atom phenomenology was observed in the rates. With multilayers as targets, the fluence dependence of the rates get Eley-Rideal-type. With a coads orbed H monolayer present, the CH3D rates at a CH3I monolayer on Pt(11 1) are affected by the suppression of hot-atom sticking. Accordingly, the rate curves exhibit similar features as expected for Eley-Rideal p henomenology. However, CH4 as a product and simultaneous abstraction o f adsorbed H via gaseous HD and H-2 formation clearly demonstrate that hot-atom reactions occur. With CH3I adsorbed on a graphite monolayer on Pt(111), the abstraction kinetics of methyl was found to agree with the operation of an Eley-Rideal mechanism. This observation is in lin e with the expectation that hot atoms do not exist on a C/Pt(111) surf ace. (C) 1998 American Institute of Physics. [S0021-9606(98)01225-2].