The Electric Quadrupole Moment of the Nucleus

Abstract

THE hyperfine structures of many terms in the arc, as well as in the first spark, spectrum of iodine show deviations from Landié's rule¹. As Murakawa has pointed out, the cause of this may be an electric quadrupole moment of the nucleus. The existence of such nuclear quadrupole moments was shown for the first time by Prof. H. Schüler and me in europium and cassiopeium². The exact theory was given by H. Casimir³. In the case of iodine the frequent occurrence of deviations leaves no doubt that they are due to the same cause. Because the electronic structure of the terms is very complicated, most of them are not suited for a determination of the quadrupole moment. The best term is 5p⁴ 6s ⁴P_5/2 of I I measured by Tolansky. Its eigenfunction is approximately the product of the 6s eigenfunction and the eigenfunction of the 5p^{4 3}P₂ term of I II. The latter can be determined from the coarse structure, using the theory of intermediate coupling. By calculations analogous to those for bismuth⁴ one gets from Casimir's formula and Tolansky's measurements a value of about 0.2 × 10²⁴ for the nuclear electric quadrupole moment of iodine. That the sign is negative, one may infer also from the term 5p³ (²D) 6s ³D₂ measured by Murakawa.