Bertha Swirles

The effect of configuration interaction on the low terms of the spectra of oxygen

The ratios of the inter-multiplet separations for the lowest states of O, O + and O ++ obtained by Slaters method depart considerably from the observed values. In this method it is assumed that matrix elements of the Hamiltonian involving two different configurations are negligible, so that each state can be described by a single configuration, whereas these matrix elements are probably appreciable, and a better approximation is obtained by use of a wave function corresponding to a superposition of more than one configuration. The effect of this superposition of configurations has been called “configuration interaction”, and the general theory of it is discussed in Condon and Shortleys Theory of atomic spectra , Chap. xv. It is shown that it occurs only between terms of the same L and S , and of the same parity (∑ l even or odd). Few quantitative applications, however, have yet been made. A calculation by Bacher for Mg shows that the effect can be considerable although the states are quite widely separated.

The Polarisabilities of Atomic Cores

If it is assumed that the series electron of an atom polarises the core, then it has been shown by Born and Heisenberg that the polarisability α of the core in a given state may be calculated from the corresponding term value by means of the approximate formulae, where q is the quantum defect, δ ν is the difference between the term and the corresponding hydrogen term, R is the Rydberg constant in cm. −1 , α 1 is the radius of first hydrogen orbit, n is the principal quantum number, k is the azimuthal quantum number, For terms with small quantum defect either of the formulae (1) and may be used, but for terms with large quantum defect (1) gives a higher degree of accuracy.