Properties of Rn-like Th$^{4+}$ from microwave spectroscopy of high-L n=37 Rydberg states of Th$^{3+}$

A recent microwave/RESIS study of n=37 Rydberg levels of Th$^{3+}$ led to the first measurements of dipole and quadrupole polarizabilities of Rn-like Th$^{4+}$ [1]. We report additional measurements that extend the data pattern to include the L=8 level and improve the precision of the L = 14 and L = 15 levels. Together these new measurements allow improved determinations of both polarizabilities and a more precise test of theoretical calculations [2].\\[4pt] [1] Julie A. Keele, S.R. Lundeen, and C.W. Fehrenbach, Phys. Rev. A \underline {83}, 062509 (2011)\\[0pt] [2] U.I Safronova and M.S. Safronova, Phys. Rev. A \underline {84}, 052515 (2011)