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Many-body perturbation theory is applied to calculate the KLL Auger rates of all terms of atoms C, N, F and Ne. Theoretical rates are compared with experiment and other theories for Ne and O. A new set of the Auger satellites, corresponding to the main photoelectron line binding energy is proposed. The intensities of these satellites are calculated and some of these satellites are identified in experimental KLL Auger spectra of Ne.

The second order ADC method to approximate the three-particle Green's function has been implemented. It allows the efficient ab initio calculation of a large number of triply ionized states of molecular systems. As an example the triple ionization spectrum of carbon monoxide is calculated and discussed with the aid of a three-hole population analysis.

The vertical double ionization spectrum of ethylene is computed using an ab-initio Green's function method. The results provide an accurate interpretation of the Auger spectrum of this molecule, showing that correlation effects are substantial and that an unexpectedly large number of doubly ionized states contributes to the spectrum.

Single orbital contributions to the total relaxation energy accompanying core ionization are computed by means of non-empirical LCAO MO SCF calculations within the ΔSCF formalism for the isoelectronic series CH4, NH3, H2O, HF and Ne. Individual contributions to the total relaxation energy associated with the valence levels of essentially core-like 2s character are also presented.

Non-empirical LCAO MO SCF calculations within the Hartree—Fock formalism have been used to investigate the variation of binding energies and relaxation energies consequent upon core ionization as a function of bond-length variation and applied electric field for the nitrogen molecule. Single orbital contributions to the total relaxation energies are presented, and are shown to give considerable insight into the electronic reorganization processes accompanying core ionization. Comparison is made throughout with results obtained in a previous study of the isoelectronic species CO. An investigation of the effect of an electric field on the potential energy surfaces of ground and core hole states, as evidenced by band profile analyses, is also considered.

This paper reports a theoretical investigation of the energy dependences of the partial photoionization cross-sections and angular distributions of photoemission for the molecules CH 4 and CF 4 . Two theoretical approaches are used for the calculation of the cross-sections. In the first, the multiple scattering Xα method (MS-Xα) is adopted, and in the latter, an extension of the additive scheme (multiple scattering with atomic amplitudes, MSAA) is employed to provide a description of the resonance structure taking into account multiple scattering of photoelectrons by the molecular potential. The main aim is to compare the results of the two theoretical approaches with the experimental data obtained using synchrotron radiation and dipole ( e , 2 e ) measurements in a wide photon energy range.

Non-empirical LCAO MO SCF computations have been carried out on the lowest energy singlet and triplet states and corresponding core hole states of the simple carbenes, CH 2 , CHF and CF 2 . An analysis is presented of changes in binding and relaxation energies for the core-ionized species and comparisons are drawn with the corresponding data for the dimers (viz. the appropriate substituted ethylenes). Changes in equilibrium geometries on core ionization have also been investigated and these suggest line broadening of the spectra arising from vibrational excitations accompanying core ionization.

Single orbital relaxation energies have been computed in the ΔSCF formalism for CO as a function of basis set. Investigations have been made of the orbital relaxation energy terms for first row atoms and correlation diagrams are presented for component relaxation terms on going from the atoms to the molecules in the particular cases of CO, N2 and NO.