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 confir ms the formation of an ethylidyne species because of the presence of v ibrational 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 specie s to be collected in the presence of high pressures (up to similar to 1 torr) of ethylene. These results reveal that ethylidyne is present o n 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, inc reases substantially by 5.3 +/- 0.4 cm(-1) torr(-1). This effect is as cribed to a loss of order in the ethylidyne layer probably caused by c o-adsorption of ethylene. (C) 1997 Elsevier Science B.V.