Reflection-absorption infrared spectroscopy of ethylene on palladium(111) at high pressure

The adsorption of ethylene adsorbed on Pd(111) at similar to 300 K is studied using reflection-absorption infrared spectroscopy which confirms the formation of an ethylidyne species because of the presence of vibrational mode at 1329 cm(-1) with a less-intense peak at 1089 cm(-1). The 1329 cm(-1) methyl mode is well away from any vibrational modes of gas-phase ethylene, which allows the spectrum of the surface species to be collected in the presence of high pressures (up to similar to 1 torr) of ethylene. These results reveal that ethylidyne is present on the surface in the presence of gas-phase ethylene and that there may be a slight increase in coverage, The width of the line, however, increases substantially by 5.3 +/- 0.4 cm(-1) torr(-1). This effect is ascribed to a loss of order in the ethylidyne layer probably caused by co-adsorption of ethylene. (C) 1997 Elsevier Science B.V.