THE INFRARED-SPECTRA OF SOME DEUTERIUM-SUBSTITUTED ETHENES CHEMISORBED ON PT(111) AND ON A PT/SIO2 CATALYST

Infrared spectra from the deuterium substituted ethenes, H2C = CD2 and D2C = CD2 adsorbed on Pt(111) at 360 K, and these plus HDC = CDH on a finely-divided Pt/SiO2 catalyst at ca. 300 K, allow a detailed analysis of the spectra from the isotopically-substituted ethylidynes. The RAIRS spectra from Pt(111) and the transmission spectra from Pt/SiO2 (limited to > 1300 cm-1) are complementary in providing information about the nu-CC/delta-CH3/delta-CD3 and the nu-CH/nu-CD regions respectively. The transmission spectra on Pt/SiO2 also provide information about additional di-sigma and pi-adsorbed species on the finely-divided catalyst. The spectra from H2C = CD2 show that there is isotopic scrambling between the adsorbed ethylidyne species, possibly mediated by the coexisting PtH/PtD species. There are indications that this does not apply to the non-dissociative di-sigma adsorbed species.