Spin relaxation of the8 S 7/2 ground state of europium in noble gases

Spin relaxation of the 4f ⁷ 6s ^{2 8} S _7/2 ground state of the Eu atom in noble gases was investigated by the direct, continuous optical pumping method. Transient signals could be observed by pulsed saturation of rf Zeeman transitions within theF= 6 hfs level of the stable Eu isotopes. The time constant of the transient signals can be related to the electronic spin depolarization cross section for Eu-noble gas collisions, yielding noble gas He Ne Ar Kr Xe σ₁in 10^?20 cm² 0.99(10) 5.1(5) 15(1.5) 43(4) 97(10) These cross sections exceed those measured forS-states of alkalies by three orders of magnitude. They can be explained by perturbations of theS-ground state configuration of Eu due to the admixture of excited state non-spherical wave functions.