Measurements in high-L, n=17 and 20 Rydberg states of barium: An investigation of ion core properties of Ba$^{+}$.*

Microwave spectroscopy studies with selective laser excitation for detection of Rydberg levels by Stark ionization have been used to measure the fine structure intervals of n=17 and 20 for a range of angular momentum states,$7\ge L\ge 11$. Measurement of the energy splittings in the fine structure levels, due largely to interactions of the Rydberg electron's angular momentum with the ion core spin, are also reported. The implications of these measurements on the determination of the ion core properties, such as the polarizability and lifetimes, and associated matrix elements is investigated.