SPECTROSCOPIC CHARACTERIZATION OF SURFACE METHYLENE ON MO(110)

The surface chemistry of diiodomethane on Mo(110) was investigated due to its potential use as a source of adsorbed methylene. We demonstrate, using high energy electron energy loss and temperature programmed reaction spectroscopy, that similar to 0.25 ML of diiodomethane undergoes C-I bond scission at 200 K, to form coadsorbed methylene and iodine. A small amount (similar to 20%) of rehydrogenation to methane occurs below 300 K, although methylene mainly decomposes to surface carbon and dihydrogen at 450 K. Interestingly, almost no methylidyne formation is observed, even as a transient surface species; consistent with facile dehydrogenation upon cleavage of the first C-H bond. The high thermal stability of the methylene moiety allows isolation of this species and definitive characterization of the vibrational signature. This is only the second proposed observation of the complete vibrational spectrum of adsorbed CH2 and, therefore, represents an important reference for future studies of adsorbed CHx species.