Electronic level structure of ${\mathrm{Th}}^{+}$ in the range of the ${}^{229m}\mathrm{Th}$ isomer energy

Abstract

Using resonant two-step laser excitation of trapped ${}^{232}{\mathrm{Th}}^{+}$ ions, we observe 166 previously unknown energy levels of even parity within the energy range from 7.8 to 9.8 eV and angular momenta from $J=1/2$ to $7/2$. We also classify the high-lying levels observed in our earlier experiments by the total angular momentum and perform ab-initio calculations to compare their results with the observed level density. The observed levels can be relevant for the excitation or decay of the ${}^{229m}\mathrm{Th}$ isomeric nuclear state which lies in this energy range. The high density of electronic levels promises a strongly enhanced electronic bridge excitation of the isomer in ${}^{229}{\mathrm{Th}}^{+}$.

10 pages, 4 figures, 4 tables; 2 figures updated, 1 reference added, section 5 updated

References in corpus (4)

• A new list of thorium and argon spectral lines in the visible
• Lifetime measurement of the ${}^{229}$Th nuclear isomer
• Excitation of the isomeric ^{229m}Th nuclear state via an electronic bridge process in ^{229}Th^+
• Nuclear clocks based on resonant excitation of gamma-transitions