The nuclear spin of arsenic

Abstract

No fine structure has yet been recorded in any of the lines of the spectra of arsenic. The present paper gives an account of the fine structures of the majority of the visible lines of As II. This spectrum is very rich in strong lines and has been observed here in the region λλ 6400-4300 with high resolving power. The gross structure multiplet analysis of As II has been made by K. R. Rao, and the fine structure observations recorded here support this analysis. The terms expected and found in this spectrum are shown in Table I. All lines involving the 4 s 2 . 4 p 2 configuration lie in the deep ultra-violet region; therefore this configuration will be disregarded in the present investigation. According to the vector coupling scheme of White and Ritsehl it will be expected that the 4 s 2 . 4 p . 5 s configuration will show wide hyperfine structure separations, since it involves an unpaired penetrating s electron; this is actually verified here with some modification. As the 4 s 2 . 4 p . 5 p configuration has no penetrating s electron, only narrow structures are to be expected, but this, however, is not observed, since structures occur in this configuration which are of the same order as those found in the previous case. This has important theoretical significance and will be discussed later. The intervals in the 4 s 2 . 4 p . 5 s triplet terms which are 3 P 0 — 3 P 1 = 397 cm. -1 and 3 P 1 — 3 P 2 = 2382 cm. -1 show that the electron coupling is by no means pure (LS) since the interval ratio deviates widely from the Landé interval rule. In the 4 s 2 . 4 p . 5 p and in the 4 s 2 . 4 p 2 terms the deviations are much less marked. This incomplete (LS) coupling affects the structure and will be considered later.