VALENCE ELECTRON MOMENTUM DISTRIBUTIONS OF ETHYLENE - COMPARISON OF EMS MEASUREMENTS WITH NEAR HARTREE-FOCK LIMIT, CONFIGURATION-INTERACTION AND DENSITY-FUNCTIONAL THEORY CALCULATIONS

The valence binding energy spectra and orbital electron momentum profiles of C2H4 have been measured by energy dispersive, multichannel, symmetric non-coplanar electron momentum spectroscopy at an impact energy of 1200 eV + binding energy. The effects of final state correlation on the valence binding energy spectrum are investigated using multi-reference singles and doubles configuration interaction calculations and the results are compared with calculations from the literature and with experiment. The measured momentum profiles are compared with cross sections calculated using a range of wavefunctions from minimal basis to essentially Hartree-Fock limit in quality. In addition, the effects of correlation and relaxation on the calculated momentum profiles are investigated using multi-reference singles and doubles configuration interaction calculations of the full ion-neutral overlap distributions. Several different configuration interaction results are investigated in the case of the 1b(3u) HOMO momentum profile. Electron correlation effects in the ground state are also examined using several density functional approaches for all the momentum profiles. The experimental momentum resolution is accounted for in all of the calculated momentum profiles by using the Gaussian-weighted planar grid procedure. The effects of vibrational averaging are investigated in the case of the 1b(3u) orbital of ethylene.