The distribution of intensity in the band spectrum of helium: the band at λ 4650

Abstract

A recent development of the analysis of the band spectrum of helium, by which the absence of certain lines in the various branches is explained and the quarter quantum numbers are replaced by half integers, makes it appear probable that alternate lines are entirely missing, i. e ., a set of rotation states is completely suppressed. Valuable information regarding this phenomenon (of which few examples are as yet known) may be expected from a study of the intensity relations in the spectrum. Such intensity relations can be predicted by expressions which have been developed of late with the aid of the correspondence principle and summation rules, but which by reason of the lack of sufficiently accurate quantitative intensity measurements have so far been little tested. It is thought that the measurements described in this paper, whilst not yet entirely free from photographic peculiarities are a sufficient improvement on those previously available, which have been obtained by eye estimation or by microphotometer, to warrant their use in a comparison with the predicted values.