Spectroscopy of high-L Rydberg levels of nickel*

The complex fine structure pattern in high-L ( L $>$ 4) Rydberg levels of nickel were studied using the Resonant Excitation Stark Ionization Spectroscopy (RESIS) technique. A beam of Ni$^{+}$ ions, obtained from a Colutron ion source, captured a single electron from a Rb 9F Rydberg target to become highly excited Rydberg levels of neutral Ni. Levels with n=9 and L=5,6,7, and 8 were excited to n=19 or 20 using a Doppler-tuned CO$_{2}$ laser, resolving the n=9 fine structure pattern, which consists of six levels for each value of L. Analysis of the pattern using the long-range polarization model determined several properties of the 3d$^{9}$ $^{2}$D$_{5/2}$ ground state of Ni$^{+}$, including its permanent quadrupole moment and its scalar and tensor dipole polarizabilities.