Fine structure in the mercury singlet terms

Abstract

The fine structure occurring in a number of line spectra has been reasonably accounted for by the theory of nuclear spin, but up to the present the complexity of the fine structure in mercury lines has remained unexplained, more lines occurring than theory demands. Because of the weakness of the singlets in the sources usually employed most of the investigations on mercury fine structure have been carried out on triplet and intercombination lines. The fine structures in the singlest series should yield more readily to analysis than in the triplet series, being simpler, and for this reason are investigated here. A comprehensive survey of the experimental work done up to 1926 in mercury was given by Ruark who succeeded in accounting for the majority of the components in several triplet lines by giving a number of levels as threefold multiplicity. Only one singlet level 6 1 P 1 was discussed and the multiplicity attributed to this was seven. In a previous communication an account was given of a method for increasing the relative and intrinsic intensity of the singlet series and of inter-combination lines involving upper singlet levels. The series 6 1 P 1 — m 1 S 0 , 7 1 S 0 — m 1 P 1 and 7 3 S 1 — m 1 P 1 are particularly strengthened and these have been examined for fine structure with a Fabry-Perot interferometer. It was stated in a preliminary note that λ 4916 (6 1 P 1 — 8 1 S 0 ) had four components and that the members of the series 7 1 S 0 — m 1 P 1 , 7 3 S 1 — m 1 P 1 were sextet. These observations are now somewhat extended, fainter components having been found. Whilst this paper was in the course of preparation, a communication was received from Venkatesachar and Sibaiya giving the structures of some of these lines. Venkatesachar also stated, that in a short note to 'Nature,' which was overlooked by the writer, Hansen found that λ 4916 was a quintet. These results will be discussed later.