Investgations of molecular interaction by photoelectron and electron energy loss spectrospies

Abstract

Electronic structures of a variety of electron donor-acceptor complexes have been studied by employing ultraviolet (HeI) photoelectron spectroscopy. The systems studied are the complexes of BH? / AlCl?, GaCl? and SO? with various electron donors and also complexes of SO? with a few electron acceptors. The results are discussed in the light of molecular orbital (MO) calculations. HeI photoelectron spectra of a few hydrogen-bonded complexes as well as of the van der Waals molecule, Xe-HCl have also been investigated. All the studies were carried out with home-built spectrometers whose design and fabrication are discussed. HeI spectra of vapor-phase complexes of BH? with H?S and H?O show that the highest occupied molecular orbitals of these systems are derived from BH?. HeI photoelectron spectra of the adducts of BF? with H?O, CH?OH, (C?H?)?O and CH?CN as well as of weak complexes of BF? with NO, H?S and CS? have been recorded in vapor phase. The results are discussed in the light of MO calculations. On complexation, the ionization energy of the fluorine lone pair orbitals of BF? is shifted in proportion to the strength of the donor-acceptor interaction. BF? seems to form a contact pair with CS?. HeI photoelectron spectra of the 1:1 adducts of AlCl? and GaCl? with (C?H?)?O in the vapor phase are presented and the bands assigned to orbital ionizations based on MO calculations. Spectra of the adducts of SO? with AlCl? and GaCl? are reported with tentative assignments. HeI photoelectron spectra of gas-phase complexes formed by SO? with the electron donors trimethylamine, diethyl ether and diethyl sulfide are recorded and the bands assigned to the different orbitals. The shift in the ionization energy of the lone pair orbital of the donor in these complexes is shown to vary proportionally with the binding energy as well as the magnitude of charge-transfer to SO?. In order to investigate situations where SO? acts as an electron donor, HeI spectrum of the complex of BF? with SO? is measured. Based on these investigations, the energy level diagrams of the complexes of BH?, BF? and SO? have been constructed. 1:1 hydrogen-bonded complexes of HCl with (C?H?)?O and SO? show marginal shifts in the ionization energies of the constituents. Photoelectron spectra of the dimers of methanol and ethanol have been obtained by employing a molecular beam photoelectron spectrometer. Orbital ordering predicted with a linear hydrogen bond geometry is in agreement with the experiment. The molecular beam spectrometer was also employed to investigate the photoelectron spectra of the van der Waals molecule Xe···HCl. While the ground state ion of the Xe-HCl van der Waals molecule is bound with a dissociation energy of 3.34 eV, some of the excited ionic states are repulsive.