The Perturbations in the Helium Band Spectrum

Abstract

The helium bands furnish an extensive material for the study of perturbations in particular for a test of the theoretical conditions, which according to Kronig must be fulfilled in order that a perturbation may occur. It was found that: I. Whenever two energy levels come close together which satisfy those conditions, a perturbation occurs. II. For those perturbations which cannot be traced to the coincidence of two known terms it can be shown that there must be as yet empirically unknown levels with the required properties to produce these perturbations. III. Whenever two levels come close together which do not satisfy Kronig's conditions, no perturbation occurs.—The nature of the observed perturbations is discussed. Only one term of each sequence is perceptibly perturbed, but at least in one case it can be clearly seen that all the levels after the perturbations are displaced by a constant amount with respect to those before the perturbation. It is also shown how the intensity anomalies may be explained.