ETHYLENE MONOLAYER AND MULTILAYER ON PT(111) BELOW 52-K - DETERMINATION OF BOND LENGTHS BY NEAR-EDGE X-RAY FINE-STRUCTURE

At temperatures lower than 52 K, ethylene condenses on Pt(111). Valence-band analysis shows that the first layer and the condensed phase exhibit almost the same positions of the molecular orbitals. Carbon K-shell excitation leads to the appearance of pi* and sigma* resonances from which it is deduced that the low temperature ethylene monolayer is pi-bonded to the substrate with minor C-C elongation, namely about 0.004 nm. A comparison is made with C-C bond lengths of ethylene monolayers and multilayers measured using NEXAFS on various substrates and given in the literature. It shows that they correlate nicely with the values of the pi-sigma parameter deduced from HREELS results for the same monolayers.