IR-SPECTRA OF CH4, CD4, C2H4, C2H2, CH3OH AND CH3OD ADSORBED ON C-60 FILMS

In the present work the IR spectra of CH4, CD4, C2H4, C2H2, CH3OH and CH3OD adsorbed on C-60 films have been studied at different temperatur es, and shifts in the resonance frequencies of the adsorbed species as compared to the gas phase were measured. In the cases of CH4, C2H4 an d C2H2, comparison of the spectral shifts in the C-H stretching region for the three molecules showed an increase in Av from methane (Delta nu = -11 cm(-1)) to ethene (Delta nu = -17 cm(-1)) and acetylene (Delt a nu = -34 cm(-1)). In all. instances the absorptions in the C-H(C-D) stretching vibration region were found to be weaker in intensity than those in the other spectral regions. With acetylene, a shoulder on the nu(5) band and a resolved shoulder on the nu(3) band were found, and were attributed to acetylene adsorbed on two different sites. Shifts i n frequency of the adsorbed molecules were noticed as the equilibrium pressure was increased. In the case of adsorbed acetylene, the shifts were attributed to lateral interactions between adsorbed C2H2 molecule s. No induced absorptions were found. In the cases of adsorbed methano l and deuteriated methanol, three absorption regions were distinguishe d in the spectrum. The frequency of the O-H stretching vibration band found at 3320 cm(-1) is similar to the absorption of liquid methanol, suggesting that CH3OH is adsorbed as clusters. In the C-H stretching r egion (3000-2700 cm(-1)), frequency shifts as compared to the gas (Del ta nu = 20-40 cm(-1)) and liquid phases (Delta nu = 6-7 cm(-1)) were m easured. The band at 1028 cm(-1), which is assigned to the C-O stretch ing vibration, persisted in part and was shifted to 1024 cm(-1) at hig her temperatures and on evacuation. From this result it is inferred th at a small fraction of methanol is either chemisorbed or physisorbed o n high-energy sites such as voids between C-60 molecules. Similar resu lts were found when deuteriated methanol (CH3OD) was adsorbed on C-60.