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Nonempirical LCAO MO SCF computations have been carried out with basis sets of double zeta quality on the ground state and core hole states of the series XCO(X = CH+3, CF+3, BH3, and BF3). Changes in binding and relaxation energies have been investigated. Single orbital contributions to relaxation energies have been computed to investigate the origin of the significant differences which are calculated for a given core hole as a function of electronic environment.

The two pairs of isomeric molecules HCN, HNC and HNO, HON have been investigated by ab initio LCAO MO SCF methods within the Hartree—Fock formalism for both ground and core ionized states. Although varying only slightly in total computed energy it is shown that substantial differences in the core hole state spectra are expected. A detailed analysis of the electronic reorganization processes accompanying core ionization in these species is given in terms of the single orbital contributions to the total relaxation energies.

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.

Individual orbital contributions to the total relaxation energies accompanying core ionizations in carbon monoxide have been computed within the ΔSCF formalism. The magnitude and sign of the contributions are shown to depend quite markedly on the localization and bonding characteristics of the orbitals concerned and vary quite significantly with bond length.

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.

Non-empirical LCAO MO SCF calculations have been carried out on the ground state and core ionized states of some hydrogen bonded dimers, and in the particular case of H2O the trimer has also been investigated. Comparison of absolute and relative binding energies and relaxation energies with respect to the corresponding monomers reveals that substantial changes occur in going to the associated species. The relaxation energies for a given core hole are shown to increase on going from monomer to dimer indicating that intermolecular contributions to relaxation energies are of the same sign irrespective of the sign for the shift in core binding energy. Creation of a core hole in the dimer species is shown to give rise to substantial changes in hydrogen bond energies compared with the neutral species. In the particular case of valence holes dominantly of 2s and 2p character it is shown that trends in shifts and relaxation energies parallel those for the core hole states.

Non-empirical LCAO MO SCF calculations within the Hartree-Fock formalism have been performed on linear and bent conformations of NiCO, for both the states arising from the 3d94s1 and 3d10 electronic configurations of Ni, for ground and core ionized species. Binding and relaxation energies are computed for the nickel atom, the free ligand (CO) and the absorbed species (NiCO). Comparison with available experimental data reveals good agreement for the shifts in core binding energies for the bent, 3d94s1 NiCO system. The main contribution to these binding energy shifts is found to be due to relaxation effects, which may be rationalized in terms of atomic population and bond overlap changes accompanying core ionization.

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.

Ab initio LCAO MO ΔSCF binding energies and relaxation energies have been computed at the STO-4.31G level for linear and branched alkanes (up to C6) and are compared with experimental data. The structural dependence of binding energies and relaxation energies is discussed, and it is concluded that binding enegy shifts in these alkanes (compared with methane) arise mainly from relaxation energy changes.

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.

Non-empirical LCAO MO SCF calculations on the ground state and localized C1s hole states of 1-propyl and 2-norbornyl carbocations have been carried out at the STO·4·31G level employing optimised geometries; the energetic preferences of the core ionized species are found to magnify energy differences which are small for the ground-state system.

Changes in binding and relaxation energies accompanying core ionizations are computed within the ΔSCF Hartree–Fock formalism for CO at the equilibrium geometry; CO at the geometries appropriate to COH+ and HCO+; COH+; HCO+(linear); HCO+(bent); HCO+(bent) with geometry appropriate to H2CO; and H2CO. Variations in relaxation energies along this series are discussed in terms of the individual valence orbital contributions to the total relaxation energies; it is found that such an analysis can provide considerable insight into the relationship between electronic structure and electronic reorganizations accompanying core ionization. Certain aspects of the energetics involved (protonation and hydrogenation in these systems) are also considered.