AN INVESTIGATION OF THE OUTERMOST ORBITAL MOMENTUM DISTRIBUTIONS OF FORMALDEHYDE, ACETALDEHYDE AND ACETONE, BY ELECTRON MOMENTUM SPECTROSCOPY AND QUANTUM-CHEMICAL CALCULATIONS AT THE SCF AND MRSD-CI LEVELS

The outermost valence electron momentum profiles have been obtained at high-momentum resolution for acetone (5b(2)) and acetaldehyde (10a'). These are compared with calculated profiles of wide ranging quality from minimal basis STO-3G to near Hartree-Fock limit SCF treatments, together with the outermost momentum profile of formaldehyde (2b(2)) measured previously by Bawagan et al. (Chem. Phys. 128 (1988) 439). The effects of the addition of diffuse functions to the basis sets are examined for a number of properties. Many-body corrections to the independent particle SCF model are evaluated by multi-reference singles and doubles configuration interaction calculations of all three molecules. These are found to give large improvements for calculated total energy but only modest gains in agreement with the observed momentum profiles. The implications for the nature of chemical bonding in these orbitals is discussed in the context of the theoretical and experimental results.