Hyperfine structure of Eu I

Abstract

A theoretical analysis is made of the hyperfine structure of the twelve levels of Eu I 4f$^7$($^8$S) 6s6p using intermediate-coupled eigenfunctions obtained from a least-squares fit of the energies of the levels. Relativistic effects for the 6p electron are calculated throughout by tensoroperator techniques. Good agreement is obtained with the observed A values, treating as parameters the polarization of the core (by the f electrons) and the hyperfine interaction constant of the 6s electron. The magnitude of the core polarization is related to data on Eu I 4f$^7$($^8$S) 6s$^2$, Eu II 4f$^7$($^8$S) 6s, and Eu III 4f$^7$($^8$S). The hyperfine-structure anomalies also fall into a consistent pattern. The observed B values are related to quadrupole moments of $^{151}$Eu and $^{153}$Eu.