Hyperfine and Zeeman Studies of Low-Lying Atomic Levels of La139 and the Nuclear Electric-Quadrupole Moment
The atomic-beam magnetic-resonance technique has been used to determine the hyperfine-interaction constants A, B, and C and electron g values gJ for all previously unstudied atomic levels of La139 below 9000 cm-1. The results are analyzed in detail in terms of a set of eigen-vectors spanning the three configurations 5d6s2, 5d26s, and 5d3. Corrections for hyperfine and Zeeman interactions between all low-lying states are carried out in intermediate coupling. The value deduced from the observed hyperfine structure for Q, the La139 nuclear ground-state electric-quadrupole moment, is influenced strongly by taking account of (a) the large recently found configuration mixing between 5d6s2, 5d26s, and 5d3 and (b) the rather substantial Sternheimer shielding effects. The effects (a) and (b), though both about 30%, are in opposite directions and partially cancel. The value obtained is Q=(+0.22+/-0.03)b. Although the order of consistency between the experimental results and theory is encouraging, a number of problems remain.