Experimental orbital momentum distributions and bonding interactions

Abstract

(e, 2e) spectroscopy has been used to obtain electron momentum distributions for the valence region of the gas-phase organometallic complex (η4-1,3-C4H6)-Fe(CO)3. The momentum distributions are compared with spherically averaged distributions calculated from ab initio SCF-MO wavefunctions for the complex at its energy optimized geometry. For binding energies of 8 to 11 eV, corresponding to ionization of electrons from molecular orbitals of the complex resulting from the interaction of C4H6 (butadiene) π and iron 3d fragment orbitals, the experimental momentum distributions are dominated by the contributions from the π HOMO of butadiene. The iron contributions to these orbitals are not readily apparent because of their small amplitude in the momentum region where the (e, 2e) experiment is sensitive. The momentum distributions at 12 to 13 eV have a distinctive double hump that is a reflection of butadiene σ orbital character. CO 5σ character appears in the momentum distributions at 14 to 15 eV.