Abstract
Recent reviews of the hyperﬁne structure of xenon and krypton have highlighted the variety of the values taken by the hyperﬁne coeﬃcients A and B of these atoms. These variations, as functions of the atomic angular momenta, were however not explained quantitatively. This article shows the simple picture and angular momentum algebra that make it possible to account for the observed trend. The only necessary approximations are to consider the interaction of the outer electron negligible with respect to the coupling of the p5 core with the nucleus, and to assume that the Racah ||(p5)j l[K]J F〉basis, conventionally used for the atomic states of noble gases, makes a ﬁtting description of the hierarchy of their angular momentum couplings. The way the calculation corroborates the apparently erratic values of hyperﬁne coeﬃcients A and B in Xe I and Kr I shows up as a conﬁrmation of the validity of these approximations.