On the arc spectrum of iodine

Abstract

Our knowledge of the arc spectrum of iodine is still very meagre, though it has been investigated by L. A. Turner in the Schumann region for the fundamental transition. He found a set of strong lines with the frequency difference of 7600 -1 cm. He showed that this is the frequency difference between the fundamental terms 2 P 3/2 , 2 P 1/2 of the 5 p 5 -level. The correctness of this value has been indirectly supported by Franck and his co-workers, from their study of the absorption spectra of alkali halides. The main difficulty in the systematization of the arc lines is due to the extremely large difference between the value of the component terms arising from any particular electron combination. Owing to this fact, lines arising from the same multiplet lie in widely different parts of the spectrum. It is difficult to make any use of the intensity rules. Moreover it appears that the Russell-Saunder or normal coupling breaks down and the ( jj )-coupling becomes operative.