Adsorption and reaction of acetylene on Ru(001): Vibrational spectroscopy and thermal desorption

Low temperature adsorption (T<130 K) of acetylene on Ru(001) and thermal evolution of the layers have been studied with HREELS and TDS. With increasing coverage, we observe a transformation from one species (I) to another (II) at 120 K. Strong similarities of the two types of spectra with those of acetylene on Ni(111) and Cu(111) on the one hand and on Pt(111), Pd(111) and Rh(111) on the other hand lead to the interpretation that acetylene initially adsorbed on μ-sites transforms to Δ-sites with increasing coverage. Mode assignment and determination of the adsorption site of the high coverage species (II) are obtained by an analysis of the angular dependences of the various loss intensities of the C₂H₂ and C₂D₂ spectra. The reaction products of the saturated layer upon heating are identified by HREELS as ethylidyne (300-340 K), vinyl groups (270-400 K) and different kinds of C-H species (270-660 K). Based on these results and 0 on comparison to organometallic cluster compound spectra we propose, a tentative reaction path for formation and decomposition of the ethylidyne species.