Spectroscopic evidence for the formation of CH_x species in the hydrogenation of carbidic carbon on Ni(100)

The CH_x species formed on Ni(100) by hydrogenation of carbidic carbon have been detected using high resolution electron energy-loss spectroscopy (HREELS). Exposures of carbidic carbon to 1×10^-7 Torr H₂ and D₂ at 313 K for 20 min produce CH_x and CD_x species, respectively. These species are identified by two energy-loss peaks for CH_x at 2970 and 1380 cm^-1 and only one peak for CD_x at 1980 cm^-1. Because of the existence of the intense peak at 1380 cm^-1, in the range of a scissors mode for CH₂ and a symmetric deformation mode for CH₃, the CH_x species are tentatively ascribed to CH₂ and/or CH₃. The CD_x species undergo decomposition at 330-370 K in UHV as well as in hydrogen below 10^-7 Torr. No stable CH_x species are observed above 400 K, which is lower than the normal reaction temperature of the methanation reaction (500 K).