ROOM-TEMPERATURE CHEMISTRY OF ACETYLENE ON PD(111) - FORMATION OF VINYLIDENE

The surface species formed following acetylene adsorption on Pd(lll) a t 300 K is identified as a vinylidene. It is oriented with its carbon- carbon axis tilted at similar to 50 degrees to the surface normal whic h allows overlap between molecular pi orbitals and the surface d-orbit als. The carbon-carbon bond is slightly longer (by similar to 0.03 Ang strom) than for adsorbed ethylene on Pd(111). This assignment is consi stent with previous photoelectron and high-resolution electron energy loss spectroscopy data. Adsorbed vinylidene decomposes to yield hydrog en and deposit carbon onto the surface at similar to 480 K with an act ivation energy of similar to 115 kJ/mol.