Energy levels of Th+ between 7.3 and 8.3 eV

TL;DR

This study identifies 43 new energy levels of Th+ ions between 7.3 and 8.3 eV using laser excitation, which could enhance nuclear excitation methods, and also determines the second ionization potential of thorium.

Contribution

The paper reports the discovery of numerous previously unknown Th+ energy levels and refines the ionization potential, advancing understanding of thorium's electronic structure.

Findings

Discovered 43 new energy levels of Th+ between 7.3 and 8.3 eV.

Inferred the second ionization potential of thorium to be between 11.9 and 12.3 eV.

Improved ion storage time by using pulsed laser photodissociation of molecular ions.

Abstract

Using resonant two-step laser excitation of trapped 232Th+ ions, we observe 43 previously unknown energy levels within the energy range from 7.3 to 8.3 eV. The high density of states promises a strongly enhanced electronic bridge excitation of the 229mTh nuclear state that is expected in this energy range. From the observation of resonantly enhanced three-photon ionization of Th+, the second ionization potential of thorium can be inferred to lie within the range between 11.9 and 12.3 eV. Pulsed laser radiation in a wide wavelength range from 237 to 289 nm is found to provide efficient photodissociation of molecular ions that are formed in reactions of Th+ with impurities in the buffer gas, leading to a significantly increased storage time for Th+ in the ion trap.