Properties of Ni$^{+}$ from microwave spectroscopy of n=9 Rydberg levels of Nickel*

The microwave/RESIS method was used to determine the relative positions of 15 of the n=9 Rydberg levels of Nickel with L $\ge $ 6. Because the ground state of the Ni$^{+}$ ion is a $^{2}$D$_{5/2}$ level, each Rydberg level (n,L) splits into six eigenstates whose relative positions are determined by long-range e-Ni$^{+}$ interactions present in addition to the dominant Coulomb interaction. A previous study with the optical RESIS method determined these positions with precision of +/- 30 MHz [1]. Using the microwave/RESIS method improves that precision by a factor of 300, and leads to much improved determinations of the Ni+ properties that control the long-range interactions. \\[4pt] [1] Julie A. Keele, Shannon L. Woods, M.E. Hanni, and S.R. Lundeen Phys. Rev. 81, 022506 (2010)