Laser resonance ionization spectroscopy of thorium

Ruohong Li; Yuan Liu; Daniel W. Stracener; Jens Lassen

doi:10.1088/1361-6455/ae1f73

Laser resonance ionization spectroscopy of thorium

Ruohong Li
, Yuan Liu
, Daniel W. Stracener
, Jens Lassen

Medical Isotopes and Development

Research output: Contribution to journal › Article › peer-review

Abstract

High-lying Rydberg and autoionizing (AI) states of thorium (Th) have been studied via resonance laser ionization spectroscopy at both TRIUMF Canada’s particle accelerator center and Oak Ridge National Lab (ORNL). Multiple Rydberg series converging to the ionization potential (IP) were observed via different stepwise laser excitation schemes and were assigned to be the 6d²7s (⁴F_3/2) np, nd, and nf series. Analysis of these series enabled the determination of the IP to be 50 868.735(54) cm⁻¹, which improved the precision by two orders of magnitude over the current adopted NIST value of 50 867(2) cm⁻¹. Additionally, four AI Rydberg series were identified and assigned to nf and nd series converging to the 6d²7s ⁴F_5/2 and 6d7s^{2 2}D_3/2 metastable states of Th⁺. The measured energies of the Rydberg and AI Rydberg states are reported, and observed perturbations within the series are discussed.

Original language	English
Article number	235003
Journal	Journal of Physics B: Atomic, Molecular and Optical Physics
Volume	58
Issue number	23
DOIs	https://doi.org/10.1088/1361-6455/ae1f73
State	Published - Dec 14 2025

Funding

The experimental work is funded by TRIUMF which receives federal funding via a contribution agreement with the National Research Council of Canada and through Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant RGP-IN-2021-02993 to R Li and SAP-IN-2017-00039 and RGP-IN-2024-05981 to J Lassen. Y Liu and D W Stracener acknowledge support from the U.S. Department of Energy, Office of Science, and Office of Nuclear Physics under Contract Number DE-AC05-00OR22725.

Keywords

autoionizing states
ionization potential
laser resonance ionization spectroscopy
Rydberg series
thorium

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title = "Laser resonance ionization spectroscopy of thorium",

abstract = "High-lying Rydberg and autoionizing (AI) states of thorium (Th) have been studied via resonance laser ionization spectroscopy at both TRIUMF Canada{\textquoteright}s particle accelerator center and Oak Ridge National Lab (ORNL). Multiple Rydberg series converging to the ionization potential (IP) were observed via different stepwise laser excitation schemes and were assigned to be the 6d27s (4F3/2) np, nd, and nf series. Analysis of these series enabled the determination of the IP to be 50 868.735(54) cm−1, which improved the precision by two orders of magnitude over the current adopted NIST value of 50 867(2) cm−1. Additionally, four AI Rydberg series were identified and assigned to nf and nd series converging to the 6d27s 4F5/2 and 6d7s2 2D3/2 metastable states of Th+. The measured energies of the Rydberg and AI Rydberg states are reported, and observed perturbations within the series are discussed.",

keywords = "autoionizing states, ionization potential, laser resonance ionization spectroscopy, Rydberg series, thorium",

author = "Ruohong Li and Yuan Liu and Stracener, \{Daniel W.\} and Jens Lassen",

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T1 - Laser resonance ionization spectroscopy of thorium

AU - Li, Ruohong

AU - Liu, Yuan

AU - Stracener, Daniel W.

AU - Lassen, Jens

PY - 2025/12/14

Y1 - 2025/12/14

N2 - High-lying Rydberg and autoionizing (AI) states of thorium (Th) have been studied via resonance laser ionization spectroscopy at both TRIUMF Canada’s particle accelerator center and Oak Ridge National Lab (ORNL). Multiple Rydberg series converging to the ionization potential (IP) were observed via different stepwise laser excitation schemes and were assigned to be the 6d27s (4F3/2) np, nd, and nf series. Analysis of these series enabled the determination of the IP to be 50 868.735(54) cm−1, which improved the precision by two orders of magnitude over the current adopted NIST value of 50 867(2) cm−1. Additionally, four AI Rydberg series were identified and assigned to nf and nd series converging to the 6d27s 4F5/2 and 6d7s2 2D3/2 metastable states of Th+. The measured energies of the Rydberg and AI Rydberg states are reported, and observed perturbations within the series are discussed.

AB - High-lying Rydberg and autoionizing (AI) states of thorium (Th) have been studied via resonance laser ionization spectroscopy at both TRIUMF Canada’s particle accelerator center and Oak Ridge National Lab (ORNL). Multiple Rydberg series converging to the ionization potential (IP) were observed via different stepwise laser excitation schemes and were assigned to be the 6d27s (4F3/2) np, nd, and nf series. Analysis of these series enabled the determination of the IP to be 50 868.735(54) cm−1, which improved the precision by two orders of magnitude over the current adopted NIST value of 50 867(2) cm−1. Additionally, four AI Rydberg series were identified and assigned to nf and nd series converging to the 6d27s 4F5/2 and 6d7s2 2D3/2 metastable states of Th+. The measured energies of the Rydberg and AI Rydberg states are reported, and observed perturbations within the series are discussed.

KW - autoionizing states

KW - ionization potential

KW - laser resonance ionization spectroscopy

KW - Rydberg series

KW - thorium

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DO - 10.1088/1361-6455/ae1f73

M3 - Article

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JO - Journal of Physics B: Atomic, Molecular and Optical Physics

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IS - 23

M1 - 235003

ER -

Laser resonance ionization spectroscopy of thorium

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