Detection of precise quantum defects of the 6snd, 6sng and 6sni Rydberg states of Ytterbium.

We use a selective field ionization technique to observe the microwave transitions of Ytterbium Rydberg states, from the 6s(n$+$3)d states to the 6sng and 6snh states for 27$\le $n$\le $33. We also observe the microwave transitions from 6snd to 6s(n$+$1)d for states 33$\le $n$\le $38. Our measurements and previous 6snd to 6s(n$+$1)d measurements give precise values for the 6snd quantum defects which indicate the presence of a previously undetected perturbation in the series. This work has been supported by the U. S. Department of Energy, Office of Basic Energy Sciences.