Abstract
Measurements of high-lying even-parity and levels of neutral are presented in this paper. Spectroscopy is performed with a two-step laser excitation from the ground state , 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 and the two-coupled even-parity series. We compare our results with the previous analysis of Aymar, Débarre, 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 is proposed for .
- Received 7 May 2018
DOI:https://doi.org/10.1103/PhysRevA.98.062506
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