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

Abstract

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).