THE KINETICS AND INFRARED SPECTROSCOPY OFC1HYDROCARBONS ADSORBED ON CLEAN AND OXYGEN-MODIFIEDMo(100)

The surface infrared spectra (700–2300cm-1) ofCH3I,CD3I,CH2I2andCD2I2adsorbed on Mo(100) at 80 K have been observed and assigned. The strongest infrared absorption ofCH3Iis theδs(CH3) mode at1236cm-1, which shifts significantly on heating the surface to 135 K, yielding a new peak at1106cm-1indicating the formation of a surface-CH3species. This new feature dominates the spectrum after annealing to 160 K and disappears at 235 K, where the TPD results show the desorption of methane. This chemistry 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. WhenCH2I2is adsorbed on Mo(100), theω(CH2) mode at1107cm-1is the strongest feature, and when one heats the sample to 135 K, a new peak appears at1061cm-1which is ascribed to the formation of a surface-CH2Ispecies. This peak disappears on heating at about 200 K, where previous ultraviolet-photoelectron-spectroscopic data showed the formation of a surface-C1species. No RAIRS data have been reported for adsorbed-methylene species, because of either a low-adsorption cross section or the lack of appropriate symmetry of these modes. The deuterated molecules show the same effects except that peaks are shifted as expected so that ν(H)/ν(D)~1.35.