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Reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) were used to identify the molecular species formed upon the reaction of hydrogen with surface carbon that is deposited by exposing acetylene to a Pt(111) surface held at 750 K. At this temperature, the acetylene is completely dehydrogenated and all hydrogen is desorbed from the surface. Upon subsequent hydrogen exposure at 85 K followed by sequential annealing to higher temperatures, ethylidyne (CCH3), ethynyl (CCH), and methylidyne (CH) are formed. The observation of these species indicates that carbon atoms and C2 molecules exist as stable species on the surface over a wide range of temperatures. Through a combination of RAIRS intensities, hydrogen TPD peak areas, and Auger electron spectroscopy, quantitative estimates of the coverages of the various species were obtained. It was found that 79% of the acetylene-derived carbon was in the form of C2 molecules, with the remainder in the form of carbon atoms. Essentially all of the acetylene-derived carbon could be hydrogenated. In contrast, 85% of an equivalent coverage of carbon deposited by ethylene exposure at 750 K was found to be inert toward hydrogenation.

The surface intermediates formed following the adsorption of acetylene (C 2 H 2 ) on Pt(111) were identified and characterized with reflection absorption infrared spectroscopy (RAIRS). It is found that isomerization of acetylene to vinylidene (CCH 2 ), followed by hydrogenation to vinyl (CHCH 2 ), precedes the formation of ethylidyne (CCH 3 ). When hydrogen and acetylene are coadsorbed on the surface, di-σ-bonded ethylene (C 2 H 4 ) and vinyl (CHCH 2 ) intermediates form at about 250 K. Vinyl is identified by its CH 2 symmetric stretch at 2988 cm -1 and CC stretch at 1280 cm -1 . The isomerization of acetylene is indicated by the formation of only one vinyl isotopomer, CDCH 2 , from the reaction of surface deuterium with C 2 H 2 . Vinyl converts to ethylidene, ethylidyne, and a high-temperature form of vinylidene at temperatures above 300 K. Ethylidyne isotopomers formed from H/D exchange when C 2 D 2 is adsorbed on the H preadsorbed surface and when C 2 H 2 is adsorbed on the D preadsorbed surface are identified by their RAIR spectra.

We have determined the number of delayed electrons emitted from an ensemble of gas-phase C60, excited at 355 nm with light from an unfocused pulsed Nd:YAG laser. Delayed electrons are detected by single particle counting and integrated over a time interval of 0.1 μs ≤ t ≤ 80 μs. At low laser fluence I, the electron number scales as I p with p = 6.0 ± 0.4. It approaches saturation at a maximum laser fluence of 100 mJ/cm2, equivalent to a power density of 14 MW/cm2, where delayed electron emission reaches a probability of 2.6 ± 1.1% per multiphoton-excited C60. This experimental value is interpreted as a lower limit to the quantum efficiency for electron emission from C60; it provides an upper limit to the efficiency of competing reactions such as dissociation of C60 into C58 + C2. The dependence of the electron number on the temperature of the fullerene source is in good agreement with the number density of C60 in the molecular beam, as computed from published equilibrium vapor pressures.