RELATIVISTIC EFFECTS ON HYPERFINE INTERACTIONS IN ALKALI METALS

A relativistic formulation of the hyperfine properties of metals has been developed and applied to study the Knight shifts Ks, relaxation times T1, and Ruderman-Kittel A12 and pseudodipolar B12 interactions in the two alkali metals, rubidium and cesium. The calculations have been carried out using Dirac orthogonalized-plane-wave wave functions, and the relativistic expressions derived have been checked for correctness by proceeding to the nonrelativistic limit. The calculated values of Ks for rubidium and cesium are 0.60% and 1.42%, as compared to 0.65% and 1.49% from experiment. The values of T1T for these metals are 1.293 and 0.128 deg sec, in good agreement with the experimental values of 1.235 and 0.130 deg sec, respectively. The relativistic values of A12 for rubidium and cesium are found to be 24.45 and 189.64 cps, as compared to 505 and 20010 cps from resonance experiments. The theoretical values of B12 for the two metals are 0.45 and 2.65 cps, respectively, as compared to 112 cycles and 355 cps from recent steady-state NMR measurements. The relativistic results for all the properties, including (T1T)-1, are substantially larger (7% to 60%) than predicted by nonrelativistic theory, leading to improved agreement with experiment. Possible reasons for the poor agreement between experiment and theory for B12 in both metals are discussed. © 1969 The American Physical Society.