AN ELECTRONIC-STRUCTURE STUDY OF ACETONE BY ELECTRON MOMENTUM SPECTROSCOPY - A COMPARISON OF SCF, MSRD-CI AND DENSITY-FUNCTIONAL THEORY

The binding energy spectra and momentum distributions of all valence orbitals of acetone have been studied by electron momentum spectroscopy (EMS) and SCF, MRSD-CI, and density functional theory (DFT) calculations. The experiment was performed using a multichannel EMS spectrometer at a total energy of 1200 eV. Binding energy spectra measured in the energy range of 6-60 eV are compared with the results of OVGF and 2ph-TDA many-body Green's function calculations. In the inner valence region strong splitting of the 5a1 and 4a1 orbitals due to finalst state electron correlation is observed. The distribution of energies and pole strengths predicted by the Green's function calculations deviates considerably from the measured ionization energies and strengths in the innervalence region. The measured momentum distributions are compared with calculations at the level of the target Hartree-Fock approximation (THFA) using the SCF method and the target Kohn-Sham approximation (TKSA) using DFT and the local-density approximation. Basis sets used for the SCF calculations ranged from the simplest (STO-3G) to large (204-GTO) and for the DFT calculations very large atomic natural orbital (ANO) basis sets were used. The effects of electron correlation and relaxation are also investigated in MRSD-CI calculations of the full ion-neutral overlap amplitude using large and saturated basis sets. In general, the THFA model with an intermediate basis set and very diffuse functions (6-311 + +G**) and with a near Hartree-Fock limit SCF wavefunction (204-GTO), and the TKSA-DFT model with an ANO basis set all provide reasonable predictions of momentum distributions for most orbitals. However, none of these calculations gives a completely satisfactory description of the momentum distribution of the HOMO (5b2) orbital.