I.H. Hillier

Bonding in some donor–acceptor complexes involving boron trifluoride. Study by means of ESCA and molecular orbital calculations

Core binding energies of a number of nitrogen bases and their adducts with BF3 are reported, and interpreted using both ab initio and semi-empirical molecular orbital calculations. The binding energies are found to reflect the change in molecular charge distribution which occurs on formation of the B—N σ bond. The correlation of the valence molecular orbitals of the complexes with those of the bases and BF3 is discussed.

Configuration interaction calculations of the Auger spectrum of CH4, HF, H2O and CO

Configuration interaction calculations of the doubly-ionized states of CH4, HF, H2O and CO are described and the results correlated with the Auger spectra of these molecules. The basis M.O.s for the configuration interaction calculations are obtained from restricted Hartree-Fock calculations on a low-lying state of the doubly ionized molecule. In general, these calculations allow an assignment of the quite complex Auger spectra of these molecules.

Ab initio molecular orbital calculations of transition metal complexes

All electron ab initio SCF-MO calculations in a better-than-minimal basis of the electronic structures of Mn(CO)5H, Mn(CO)5CH3, Mn(CO)5Cl and Mn(CO)5CN are reported. The nature of the bonding of the CO groups, and of the other ligand to the central metal atom is discussed, together with the effect of the substituent on the electronic structure of the carbonyl ligands. The calculated wavefunctions are used to discuss the low energy photoelectron spectra, and other experimental data on these molecules.

High energy photoelectron spectroscopy of transition metal complexes. Part 1.—Bonding in substituted and unsubstituted first row carbonyls

Core electron binding energies of a series of substituted and unsubstituted transition metal carbonyls are reported and interpreted using both ab initio and approximate molecular orbital calculations. The ESCA chemical shifts observed upon substitution are well reproduced by such calculations, although the rather poor prediction of the change in CO core binding energies on complex formation, together with the observation of unusually intense satellite peaks in the photoelectron spectra of the carbonyls suggests that orbital relaxation may be greater in complexed than in free CO.

A configuration interaction calculation of the potential energy surface of Li3

Large-scale configuration interaction calculations of the potential energy surface of Li3 are described. The major prediction which emerges is that triangular configurations are more stable than linear ones, with the 2B2 and 2A1 states having different equilibrium geometries but essentially the same energies. It is found that the most stable linear configuration is symmetric, unlike the prediction of restricted Hartree-Fock calculations. A fit of our calculated surface to a semi-empirical LEPS function is presented.

A theoretical study of the adsorption of simple molecules on MgO surfaces: CO, HCO, HOC, H2CO, HCOH, CH2OH and CH3O

Abstract The adsorption of a series of molecules at the (001) surface of MgO and at an impurity Cu + ion therein has been studied by means of a combination of ab initio molecular orbital and lattice defect methods. The molecular species investigated include CO, HCO, HOC, H 2 CO and HCOH, and CH 3 O and CH 2 OH, all of potential importance in CO/H 2 chemistry. Binding energies of each species adsorbing either through carbon or oxygen have been derived from SCF studies using split-valence basis sets throughout. Additional calculations involving more flexible basis sets, with incorporation of electron correlation have also been performed. Binding through oxygen leads to very similar relative stabilities of the minima on both [CH 2 O] and [CH 3 O] potential energy surfaces to those predicted for the “free” gas-phase species, and is in general the energetically preferred mode of interaction when binding with an Mg 2+ ion of the non-defective surface. Binding through carbon is the energetically preferred path in interactions with the Cu + dopant ion, however, leading to significant changes in the “free” species energetics. This enhanced binding is attributed to the contribution from π back-donation, an effect which is of importance only in interactions with the dopant ion and which is found to be sensitive to the incorporation of electron correlation.

Configuration interaction calculations of the satellite peaks associated with Cls ionization of carbon monoxide

Large scale configuration interaction calculations of the first five 2Σ+ carbon 1s core hole states of CO are described. Configuration selection, by means of perturbation theory, from ≳30 000 bonded functions yields final transition energies in good agreement with experiment. The inadequacy of a CI expansion including only singly excited configurations from the RHF reference configuration, is shown. A small CI expansion, using selected configurations, yields calculated intensities sufficiently accurate to allow an assignment of the experimental spectrum which is not possible from the calculated transition energies alone.

Satellite peaks in the high energy photoelectron spectra of some small first row molecules

The gas phase high energy photoelectron spectra of CH4, NH3, H2O, N2, O2, CO and CO2 have been recorded, and in all cases weak satellite peaks to high binding energy of the main ionization peak are observed. These peaks are assigned to transitions to ionic states in which valence electron excitation as well as core ionization has occurred. The intensity and position of these peaks, relative to the main ionization peak have been estimated from ab initio UHF calculations on the core hole states, which in general allow assignment of the satellite peaks in terms of orbital transitions of the core hole ion.

Electron correlation and the nature of the sextuple bond in the dimolybdenum molecule

Abstract The potential energy curve for the 1 Σ g + state of Mo 2 has been generated by a variety of configuration interaction treatments. The inadequacy of the single determinantal, and double-excitation CI treatments is demonstrated, inclusion of higher-order excitations is essential to give bonding with respect to 2Mo ( 7 S). The calculations suggest that the bond order of six is significantly reduced upon inclusion of correlation.

Correlation effects and the 1s hole satellite spectrum of N2

Abstract Large scale CI calculations are used to predict the positions of the low lying satellite peaks associated with 1s ionization of N 2 . Multiply excited configurations are shown to be important in the interpretation of the satellite spectrum and a new assignment of the third and fourth observed satellites is proposed. A small scale CI calculation, including those configurations found to be important from the large scale calculation is used to interpret most of the peaks in the satellite spectrum, and also to compute their intensities. It is found that configuration interaction in the ground state of N 2 results in a large change in the predicted intensity of the second satellite peak.