NEXAFS IDENTIFICATION OF A CATALYTIC REACTION INTERMEDIATE - C4H4 ON PD(111)

Polarisation-dependent NEXAFS data are presented for the reaction inte rmediate C4H4 chemisorbed on Pd(III). Comparison of these data with ca lculated spectra indicates that this species is a metallocycle with sl ightly expanded (approximately 0.05 angstrom) C-C bonds. Dependence of the resonance intensities on photon incidence angle shows that the mo lecular plane is tilted at approximately 35-degrees with respect to th e metal surface. The assigned chemical identity and absorption geometr y are fully consistent with all the reactive behaviour of C4H4.