The kinetics and infrared spectroscopy of C-1 hydrocarbons adsorbed on clean and oxygen-modified Mo(100)

The surface infrared spectra (700-2300 cm(-1)) of CH3I, CD3I, CH2I2 and CD2 I2 adsorbed on Mo(100) at 80 K have been observed and assigned. The stronge st infrared absorption of CH3I is the delta(s)(CH3) mode at 1236 cm(-1), wh ich shifts significantly on heating the surface to 135 K, yielding a new pe ak at 1106 cm(-1) indicating the formation of a surface-CH3 species. This n ew feature dominates the spectrum after annealing to 160 K and disappears a t 235 K, where the TPD results show the desorption of methane. This chemist ry was also studied on oxygen-covered Mo(100) with oxygen coverages of 1.0 and 1.5. These were not found to substantially affect the surface chemistry . When CH2I2 is adsorbed on Mo(100), the omega(CH2) mode at 1107 cm(-1) is the strongest feature, and when one heats the sample to 135 K, a new peak a ppears at 1061 cm(-1) which is ascribed to the formation of a surface-CH2I species. This peak disappears on heating at about 200 K, where previous ult raviolet-photoelectron-spectroscopic data showed the formation of a surface -C-1 species. No RAIRS data have been reported for adsorbed-methylene speci es, because of either a low-adsorption cross section or the lack of appropr iate symmetry of these modes. The deuterated molecules show the same effect s except that peaks are shifted as expected so that nu(H)/nu(D) similar to 1.35.