Chemistry of Cyclopropane on Pt(111): Thermal, Electron, and Photon Activation

The thermal, electron, and photon-induced chemistry of cyclopropane, c-C 3 H 6, adsorbed on Pt(111) at 100 K has been studied. The thermal chemistry is simple. Adsorption is saturable, no multilayer accumulates, and thermal desorption exhibits only c-C 3 H 6 with one peak at 144 K. High-resolution electron energy loss spectra results indicate that c-C 3 H 6 adsorbs with the plane of the ring tilted away from the surface normal. The electron-induced chemistry is more complex. Irradiation with 50 eV electrons activates dissociation of adsorbed c-C 3 H 6 at 100 K, and there are thermally activated reactions during subsequent temperature-programmed desorption. The total cross-section for destruction of c-C 3 H 6 is 8.2 (±0.2) × 10 -17 cm 2 . For low electron fluences, <10 16 cm -2, the chemistry involved is describable in terms of C−C bond breaking to open the ring and form metallacyclic species, some of which promptly lose H to form allylic (C 3 H 5 ) moieties. In subsequent thermally activated reaction-limited processes, propylene, methane, ethylene, and hydrogen desorb. Only carbon remains above 800 K. Activation with 6.4 eV (193 nm) photons is also effective, but the cross section for loss of c-C 3 H 6 is nearly 4 orders of magnitude lower than that for electron irradiation.