III. Further measurements upon the fine structures in the first spark spectrum

Abstract

In an earlier paper by Tolansky (1935 a ) measurements were given for the fine structures of forty-two lines in the visible region of the first spark spectrum of iodine. Of these eleven had then been classified by Murakawa (1933). It was proved that the nuclear spin of iodine is 5/2. After these measurements had been communicated, Lacroute (1934) published an extensive analysis of the gross structure multiplets in the I + spectrum, the Zeeman effect being used as a guide. Lacroute established the positions of groups of terms going to the 4 S, 2 D and 2 P series limits, the electron configurations involved being 5 s 2 5 p 4 , 5 s 2 5 p 3 6 p , 5 s 2 5 p 3 6 s , 5 s 2 5 p 3 5 d , 5 s 2 5 p 3 7 s , 5 s 2 5 p 3 6 d , 5 s 2 5 p 3 7 s . The eleven classified lines, whose fine structures had been analysed, were found to arise from transitions between terms going to the 4 S series limit only. Fourteen of the remaining lines were classified by Lacroute who showed that they belong to the 2 D system. A fine-structure analysis for these additional lines was then made by Tolansky (1935 b ). No intercombination lines between the two systems were available and the analysis proved to be difficult, with resulting ambiguity, in a number of the interval factors calculated. This we now know to be due to the existence of unexpectedly large interval factors in the 6 p and 5 d configurations (in what follows the 5 s 2 5 p 3 group of electrons is omitted from the electron designations for the sake of brevity). A further complication exists due to the occurrence of perturbation. Since the question of perturbations is of particular importance in connexion with the determination of a possible nuclear electrical quadrupole moment, it seemed desirable to extend the earlier measurements down into the ultra-violet region where strong intercombination lines appear. Since the earlier measurements were all made with a silvered Fabry-Perot interferometer, very accurate measurements could only be made up to the blue-green. To extend these into the ultra-violet, and to improve the previous measurements made in the blue and violet, we have made use of an exceptionally good quartz Lummer plate, a variable gap aluminized Fabry-Perot interferometer, and also a 21 ft. grating used up to the fourth order.