VARIABLE-ENERGY PHOTOELECTRON-SPECTROSCOPY OF (ETA(5)-C5H5)M(ETA(3)-C3H5) (M=NI AND PD) - MOLECULAR-ORBITAL ASSIGNMENTS

Variable-energy photoelectron spectra have been recorded between 21.2 and 70 eV photon energies for (eta(5)-C5H5)Ni(eta(3)-C3H5) and between 21.2 and 60 eV photon energies for (eta(5)-C5H5)Pd(eta(3)-C3H5). The ground-state electronic structures have been calculated with the XQ-SW method. Photoionization cross sections (sigma) have also been calcula ted for the valence ionizations using both the Gelius and X alpha-SW m ethods, and the theoretical branching ratios (sigma(i)/Sigma sigma) ha ve been compared with the observed photoelectron branching ratios (A(i )/Sigma A, A = band area). The assignments of the photoelectron spectr a are based on comparison of the experimental and theoretical band ene rgies and intensities. For both molecules, the lowest binding energy p eak is assigned to the HOMO with mainly metal d-Cp pi(2) bonding chara cter. The higher IP's for the Pd 4d electrons lead to a different assi gnment for the second peaks in the two compounds; this orbital has mai nly Ni 3d character for M = Ni but has high pi-allyl character for M = Pd. The metal d orbitals and ligand pi orbitals follow at higher bind ing energies.