Laser and microwave spectroscopy of even-parity Rydberg states of neutral ytterbium and multichannel-quantum-defect-theory analysis

Abstract

Measurements of high-lying even-parity $6sns\phantom{\rule{0.16em}{0ex}}{}^{1}{S}_{0}$ and $6snd\phantom{\rule{0.16em}{0ex}}{}^{1,3}{D}_{2}$ levels of neutral $^{174}\mathrm{Yb}$ are presented in this paper. Spectroscopy is performed with a two-step laser excitation from the ground state $4{f}^{14}6{s}^{2}\phantom{\rule{0.16em}{0ex}}{}^{1}{S}_{0}$, 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, D\'ebarre, 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 ${I}_{6s}=50443.07041(25)\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ is proposed for $^{174}\mathrm{Yb}$.