EMS STUDIES OF LARGER MOLECULES OF CHEMICAL AND BIOCHEMICAL INTEREST

The challenges involved in extending electron momentum spectroscopy (E MS) studies beyond small polyatomic molecules to more complicated syst ems are discussed. EMS results for the highest occupied (frontier) mol ecular orbitals of glycine (NH2CH2COOH) and dimethoxymethane ((CH3O)(2 )CH2) demonstrate possible approaches to overcoming such challenges as closely spaced valence orbitals, low volatility, and the conformation al mobility of the target compound. The increased sensitivity availabl e from recently developed multichannel electron momentum spectrometers is a key factor in overcoming these challenges and making such EMS st udies feasible. The utility of Kohn-Sham density functional theory (DF T) for EMS calculations on larger molecules such as glycine and dimeth oxymethane using the recently formulated target Kohn-Sham approximatio n is also investigated as experimental momentum profiles are compared with theoretical momentum profiles generated via Kohn-Sham DFT and a r ange of Hartree-Fock calculations. The Kohn-Sham DFT calculations prov ide better agreement with experiment for the frontier orbitals of glyc ine and dimethoxymethane than even the near Hartree-Fock limit results .