Chemistry of cyclopropane on Pt(111): Thermal, electron, and photon activation

The thermal, electron, and photon-induced chemistry of cyclopropane, c-C3H6 , adsorbed on Pt(111) at 100 K has been studied. The thermal chemistry is s imple. Adsorption is saturable, no multilayer accumulates, and thermal deso rption exhibits only c-C3H6 with one peak at 144 K. High-resolution electro n energy loss spectra results indicate that c-C3H6 adsorbs with the plane o f the ring tilted away from the surface normal. The electron-induced chemis try is more complex. Irradiation with 50 eV electrons activates dissociatio n of adsorbed c-C3H6 at 100 K, and there are thermally activated reactions during subsequent temperature-programmed desorption. The total cross-sectio n for destruction of c-C3H6 is 8.2 (+/-0.2) x 10(-17) cm(2). For low electr on 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 (C3H5) moieties. In subsequent th ermally 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- C3H6 is nearly 4 orders of magnitude lower than that for electron irradiati on.