ELECTRON LOCALIZATION IN THE BIS-ARENE COMPLEXES [(ETA-C6H6)2CR] AND [(ETA-C6H5ME)2MO] - AN INVESTIGATION BY PHOTOELECTRON-SPECTROSCOPY WITH VARIABLE PHOTON ENERGY

Relative partial photoionization cross sections have been measured for the valence bands of [(eta-C6H6)2Cr] and [(eta-C6H5Me)2Mo] over the photon energy ranges 24-80 eV ([(eta-C6H6)2Cr]) and 24-100 eV ([(eta-C6H5Me)2Mo]). Both compounds show pronounced intensity increases of the metal-based ionizations (a1g-1 and e2g-1) in the region of the np subshell ionization potentials, attributable to nd resonant photoemission following np-->nd giant resonant absorption. Shape resonances are also observed in the cross sections of these bands. For [(eta-C6H5Me)2Mo], the two resonance processes are almost coincident in photon energy, but can be distinguished more clearly in the [(eta-C6H6)2Cr] cross sections. Evidence for metal d-carbon 2p-pi covalency in the e1g set of molecular orbitals is found, with features in the cross sections of the metal-based bands correlating with those in the e1g-1 ionizations. The e1u-1 bands show an essentially monotonic cross section decrease with photon energy.