Title:

The electronic structure of atoms and diatomic hydrides

In Part I of this thesis the theory of the isoelectronic structure of atoms is discussed using the notion of an isoelectronic sequence in which the electronic energy is expressed as a perturbation expansion in terms of inverse powers of the nuclear charge. An empirical procedure is then developed in order to estimate the second and third order coefficients of this expansion, from which the nuclear magnetic shielding constants and ionization potentials are. calculated.
Part II extends the theory of isoelectronic sequences of atoms to the calculation of the first order density matrix. It is shown that to first order the calculation of this matrix can be reduced to the solution of a number of oneelectron equations which have been solved for the helium ground and 3S states and also the lithium ground state. For these atoms mean values of oneelectron operators have been calculated by integration of this density matrix. From the density matrix the natural orbitals also can be derived, and are found to be identical to first order with the unrestricted molecular orbitals.
The third part reviews the role of united atom theory as applied to light molecules* The Platt Electrostatic model of a diatomic hydride is modified by introducing a scale factor which depends on the internuclear distance* This enables the molecular virial theorem to be satisfied, improves the agreement with experiment of the internuclear distance and force constant, and still enables the theory to be interpreted electrostatically*
Part IV extends the theory of isoelectronic sequences to diatomic hydrides, using a scale factor which varies with both the charge of the second nucleus and internuclear distance. The energies to first order, the equilibrium internuclear distances and force constants are computed for some isoeleetronic sequences and compared with experiment.
