Polarizabilities of Rn-like Th4+ from rf spectroscopy of Th3+ Rydberg   levels
  High resolution studies of the fine structure pattern in high-L n=37 levels of Th3+ have been carried out using radio-frequency (rf) spectroscopy detected with Resonant Excitation Stark Ionization Spectroscopy (RESIS). Intervals separating L=9 to L=15 levels have been measured, and the results analyzed with the long-range effective potential model. The dipole polarizability of Th4+is determined to be aD= 7.720(7) a.u.. The quadrupole polarizability is found to be 21.5(3.9) a.u. Both measurements represent significant tests of a-priori theoretical descriptions of this highly relativistic ion. 
J.A. Keele (1), S.R. Lundeen (1), C.W. Fehrenbach (2) ((1) Colorado   State University, (2) Kansas State University)
physics.atom-ph