Laser And Microwave Spectroscopy Of Even-Parity Rydberg States Of Neutral Ytterbium And Multichannel-Quantum-Defect-Theory Analysis

Measurements of high-lying even-parity 6sns(1)S(0) and 6snd(1,3)D(2) levels of neutral Yb-174 are presented in this paper. Spectroscopy is performed with a two-step laser excitation from the ground state 4f(14)6s(2) S-1(0), and the Rydberg levels are detected by using the field ionization method. Additional two-photon microwave spectroscopy is used to improve the relative energy accuracy where possible. The spectroscopic measurements are complemented by a multichannel-quantum-defect-theory (MQDT) analysis for the J = 0 and the two-coupled J = 2 even-parity series. We compare our results with the previous analysis of Aymar, Debarre, and Robaux [J. Phys. B: At. Mol. Phys. 13, 1089 (1980)] and analyze the observed differences. From the MQDT models, a revised value for the first ionization limit I-6s = 50443.07041(25) cm(-1) is proposed for Yb-174.