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Laser-fluence-dependent production of molecular thorium ions in different charge states for trapped-ion experiments

Jonas Stricker1,2,3,*, Jean Velten1, Valerii Andriushkov2,3,4, Lennard M. Arndt1, Dmitry Budker2,3,4,5, Konstantin Gaul3,4, Dennis Renisch1,2,3, Ferdinand Schmidt-Kaler2,3,4, Azer Trimeche4 et al. (TACTICa Collaboration)

Azer Trimeche4, Lars von der Wense4, and Christoph E. Düllmann1,2,3,6 (TACTICa Collaboration)

  • *Contact author: jostrick@uni-mainz.de; superheavies.de
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Phys. Rev. A 112, 012821 – Published 24 July, 2025

DOI: https://doi.org/10.1103/ztxz-dwhk

Abstract

Thorium ions and molecules, recognized for their distinctive nuclear and atomic attributes, are central to numerous trapped-ion experiments globally. Our study introduces an effective, compact source of thorium atomic and molecular ions produced via laser ablation of microgram-scale, salt-based samples. We thoroughly analyze the variety of ion species and charge states generated at varying laser fluences. Utilizing 10 µg of thorium fluoride crystals and laser fluences between 1.00(5) and 6.75(35) J/cm2, we produce thorium molecular ions ThFx232n+ (with x=0–3 and charge states up to n=3), including ThF2+ and ThF3+. These species are particularly relevant for spectroscopy; ThF3+ is valuable due to its stable closed-shell configuration, while ThF2+, which is isoelectronic to RaF, offers a unique probe for studying nuclear structure and fundamental symmetries due to its simple electronic structure with a single unpaired electron. Density-functional-theory-based calculations of the electric charge distribution aid in understanding the formation of the observed species. Positive charges are found to be mainly located on the thorium atom, which points to an inhibition of immediate Coulomb explosion, thus supporting the existence of the observed ion species. The simplicity of the method and similarities among the actinide elements suggest that our approach will also be applicable to other actinide species.

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References (69)

  1. J. Tiedau, M. V. Okhapkin, K. Zhang, J. Thielking, G. Zitzer, E. Peik, F. Schaden, T. Pronebner, I. Morawetz, L. T. De Col, F. Schneider, A. Leitner, M. Pressler, G. A. Kazakov, K. Beeks, T. Sikorsky, and T. Schumm, Laser excitation of the Th-229 nucleus, Phys. Rev. Lett. 132, 182501 (2024).
  2. R. Elwell, C. Schneider, J. Jeet, J. E. S. Terhune, H. W. T. Morgan, A. N. Alexandrova, H. B. Tran Tan, A. Derevianko, and E. R. Hudson, Laser excitation of Th229 the isomeric transition in a solid-state host, Phys. Rev. Lett. 133, 013201 (2024).
  3. C. Zhang, T. Ooi, J. S. Higgins, J. F. Doyle, L. von der Wense, K. Beeks, A. Leitner, G. A. Kazakov, P. Li, P. G. Thirolf et al., Frequency ratio of the Th229 nuclear isomeric transition and the Sr87 atomic clock, Nature (London) 633, 63 (2024).
  4. E. Peik and C. Tamm, Nuclear laser spectroscopy of the 3.5 eV transition in Th-229, Europhys. Lett. 61, 181 (2003).
  5. W. G. Rellergert, D. DeMille, R. R. Greco, M. P. Hehlen, J. R. Torgerson, and E. R. Hudson, Constraining the evolution of the fundamental constants with a solid-state optical frequency reference based on the Th229 nucleus, Phys. Rev. Lett. 104, 200802 (2010).
  6. C. J. Campbell, A. G. Radnaev, A. Kuzmich, V. A. Dzuba, V. V. Flambaum, and A. Derevianko, Single-ion nuclear clock for metrology at the 19th decimal place, Phys. Rev. Lett. 108, 120802 (2012).
  7. V. V. Flambaum, Enhanced effect of temporal variation of the fine structure constant and the strong interaction in Th229, Phys. Rev. Lett. 97, 092502 (2006).
  8. K. Beeks, G. A. Kazakov, F. Schaden, I. Morawetz et al., Fine-structure constant sensitivity of the Th229 nuclear clock transition, arXiv:2407.17300
  9. D. Antypas, O. Tretiak, K. Zhang, A. Garcon, G. Perez, M. G. Kozlov, S. Schiller, and D. Budker, Probing fast oscillating scalar dark matter with atoms and molecules, Quantum Sci. Technol. 6, 034001 (2021).
  10. E. R. Meyer and J. L. Bohn, Prospects for an electron electric-dipole moment search in metastable ThO and ThF+, Phys. Rev. A 78, 010502(R) (2008).
  11. L. V. Skripnikov, A. N. Petrov, and A. V. Titov, Communication: Theoretical study of ThO for the electron electric dipole moment search, J. Chem. Phys. 139, 221103 (2013).
  12. T. Fleig and M. K. Nayak, Electron electric dipole moment and hyperfine interaction constants for ThO, J. Mol. Spectrosc. 300, 16 (2014).
  13. V. V. Flambaum, D. DeMille, and M. G. Kozlov, Time-reversal symmetry violation in molecules induced by nuclear magnetic quadrupole moments, Phys. Rev. Lett. 113, 103003 (2014).
  14. M. Denis, M. S. Norby, H. J. A. Jensen, A. S. P. Gomes, M. K. Nayak, S. Knecht, and T. Fleig, Theoretical study on ThF+, a prospective system in search of time-reversal violation, New J. Phys. 17, 043005 (2015).
  15. L. V. Skripnikov and A. V. Titov, Theoretical study of ThF+ in the search T,P-violation effects: Effective state of a Th atom in ThF+ and ThO compounds, Phys. Rev. A 91, 042504 (2015).
  16. M. Denis and T. Fleig, In search of discrete symmetry violations beyond the standard model: Thorium monoxide reloaded, J. Chem. Phys. 145, 214307 (2016).
  17. N. R. Hutzler, A. Borschevsky, D. Budker et al., Searches for new sources of CP violation using molecules as quantum sensors, arXiv:2010.08709.
  18. V. V. Flambaum, Enhanced nuclear Schiff moment and time-reversal violation in Th229-containing molecules, Phys. Rev. C 99, 035501 (2019).
  19. B. J. Barker, I. O. Antonov, M. C. Heaven, and K. A. Peterson, Spectroscopic investigations of ThF and ThF+, J. Chem. Phys. 136, 104305 (2012).
  20. K. B. Ng, Y. Zhou, L. Cheng, N. Schlossberger, S. Y. Park, T. S. Roussy, L. Caldwell, Y. Shagam, A. J. Vigil, E. A. Cornell, and J. Ye, Spectroscopy on the electron-electric-dipole-moment–sensitive states of ThF+, Phys. Rev. A 105, 022823 (2022).
  21. Y. Zhou, K. B. Ng, L. Cheng, D. N. Gresh, R. W. Field, J. Ye, and E. A. Cornell, Visible and ultraviolet laser spectroscopy of ThF, J. Mol. Spectrosc. 358, 1 (2019).
  22. C. Zülch, K. Gaul, S. M. Giesen, R. F. Garcia Ruiz, and R. Berger, Cool molecular highly charged ions for precision tests of fundamental physics, arXiv:2203.10333.
  23. T. A. Isaev, S. Hoekstra, and R. Berger, Laser-cooled RaF as a promising candidate to measure molecular parity violation, Phys. Rev. A 82, 052521 (2010).
  24. T. A. Isaev and R. Berger, Lasercooled radium monofluoride: A molecular all-in-one probe for new physics, arXiv:1302.5682.
  25. S. M. Udrescu, A. J. Brinson, R. F. Garcia Ruiz et al., Isotope shifts of radium monofluoride molecules, Phys. Rev. Lett. 127, 033001 (2021).
  26. S. G. Wilkins, S. M. Udrescu, M. Athanasakis-Kaklamanakis et al., Observation of the distribution of nuclear magnetization in a molecule, arXiv:2311.04121.
  27. R. F. Garcia Ruiz, R. Berger, J. Billowes et al., Spectroscopy of short-lived radioactive molecules, Nature (London) 581, 396 (2020).
  28. G. Arrowsmith-Kron, M. Athanasakis-Kaklamanakis, M. Au et al., Opportunities for fundamental physics research with radioactive molecules, Rep. Prog. Phys. 87, 084301 (2024).
  29. C. J. Campbell, A. V. Steele, L. R. Churchill, M. V. DePalatis, D. E. Naylor, D. N. Matsukevich, A. Kuzmich, and M. S. Chapman, Multiply charged thorium crystals for nuclear laser spectroscopy, Phys. Rev. Lett. 102, 233004 (2009).
  30. K. Zimmermann, M. V. Okhapkin, O. A. Herrera-Sancho, and E. Peik, Laser ablation loading of a radiofrequency ion trap, Appl. Phys. B 107, 883 (2012).
  31. V. I. Troyan, P. V. Borisyuk, R. R. Khalitov, A. V. Krasavin, Y. Y. Lebedinskii, V. G. Palchikov, S. S. Poteshin, A. A. Sysoev, and V. P. Yakovlev, Generation of thorium ions by laser ablation and inductively coupled plasma techniques for optical nuclear spectroscopy, Laser Phys. Lett. 10, 105301 (2013).
  32. P. V. Borisyuk, S. P. Derevyashkin, K. Yu Khabarova, N. N. Kolachevsky, Y. Y. Lebedinsky, S. S. Poteshin, A. A. Sysoev, E. V. Tkalya, D. O. Tregubov, V. I. Troyan, O. S. Vasiliev, and V. P. Yakovlev, Method of the production and trapping of thorium ions for nuclear transition investigation, J. Phys.: Conf. Ser. 941, 012107 (2017).
  33. M. Piotrowski, J. Scarabel, M. Lobino, E. Streed, and S. Gensemer, Studies of thorium and ytterbium ion trap loading from laser ablation for gravity monitoring with nuclear clocks, OSA Continuum 3, 2210 (2020).
  34. K. Groot-Berning, F. Stopp, G. Jacob, D. Budker, R. Haas, D. Renisch, J. Runke, P. Thörle-Pospiech, Ch. E. Düllmann, and F. Schmidt-Kaler, Trapping and sympathetic cooling of single thorium ions for spectroscopy, Phys. Rev. A 99, 023420 (2019).
  35. F. Stopp, K. Groot-Berning, G. Jacob, D. Budker, R. Haas, D. Renisch, J. Runke, P. Thörle-Pospiech, Ch. E. Düllmann, and F. Schmidt-Kaler, Catching, trapping and in-situ-identification of thorium ions inside coulomb crystals of Ca40+ ions, Hyperfine Interact. 240, 33 (2019).
  36. C. J. Campbell, A. G. Radnaev, and A. Kuzmich, Wigner crystals of Th229 for optical excitation of the nuclear isomer, Phys. Rev. Lett. 106, 223001 (2011).
  37. J. Thielking, M. V. Okhapkin, P. Głowacki, D. M. Meier, L. von der Wense, B. Seiferle, Ch. E. Düllmann, P. G. Thirolf, and E. Peik, Laser spectroscopic characterization of the nuclear-clock isomer Th229m, Nature (London) 556, 321 (2018).
  38. Z. Li, L. Li, X. Hua, and X. Tong, Loading and identifying various charged thorium ions in a linear ion trap with a time-of-flight mass spectrometer, J. Appl. Phys. 135, 144402 (2024).
  39. P. Fischer, J. Stricker, Ch. E. Düllmann, D. Renisch, and L. Schweikhard, Gas-phase thorium clusters from laser ablation suggest magicity of Th13+, Eur. Phys. J. D 79, 30 (2025).
  40. P. Fischer, J. Stricker, Ch. E. Düllmann, D. Renisch, L. Schweikhard, and C. Tantardini, Gas-phase thorium molecules from laser ablation, Phys. Rev. Res. 6, 043317 (2024).
  41. D.-T. Nguyen, T. Steimle, C. Linton, and L. Cheng, Optical Stark and Zeeman spectroscopy of thorium fluoride (ThF) and thorium chloride (ThCl), J. Phys. Chem. A 123, 1423 (2019).
  42. M. Au, M. Athanasakis-Kaklamanakis, L. Nies, J. Ballof, R. Berger, K. Chrysalidis, P. Fischer, R. Heinke, J. Johnson, U. Köster, D. Leimbach, B. Marsh, M. Mougeot, B. Reich, J. Reilly, E. Reis, M. Schlaich, C. Schweiger, L. Schweikhard, S. Stegemann et al., In-source and in-trap formation of molecular ions in the actinide mass range at CERN-ISOLDE, Nucl. Instrum. Methods Phys. Res. Sect. B 541, 375 (2023).
  43. M. Au, L. Nies, S. Stegemann, M. Athanasakis-Kaklamanakis, T. E. Cocolios, P. Fischer, P. F. Giesel, J. D. Johnson, U. Köster, D. Lange, M. Mougeot, J. Reilly, M. Schlaich, C. Schweiger, L. Schweikhard, F. Wienholtz, W. Wojtaczka, Ch. E. Düllmann, and S. Rothe, Production and purification of molecular Ac225 at CERN-ISOLDE, J. Radioanal. Nucl. Chem. 334, 367 (2024).
  44. A. R. Bubas, C. J. Owen, and P. Armentrout, Reactions of atomic thorium and uranium cations with CF4 studied by guided ion beam tandem mass spectrometry, Int. J. Mass Spectrom. 472, 116778 (2022).
  45. D. Wanless, Electron-ion recombination in argon, J. Phys. B 4, 522 (1971).
  46. N. R. Hutzler, H.-I. Lu, and J. M. Doyle, The buffer gas beam: An intense, cold, and slow source for atoms and molecules, Chem. Rev. 112, 4803 (2012).
  47. D. Schröder, M. Diefenbach, T. M. Klapötke, and H. Schwarz, UF3+—A thermochemically stable diatomic trication with a covalent bond, Angew. Chem. Int. Ed. 38, 137 (1999).
  48. R. Haas, T. Kieck, D. Budker, Ch. E. Düllmann, K. Groot-Berning, W. Li, D. Renisch, F. Schmidt-Kaler, F. Stopp, and A. Viatkina, Development of a recoil ion source providing slow Th ions including Th229(m) in a broad charge state distribution, Hyperfine Interact. 241, 25 (2019).
  49. See Supplemental Material at http://link.aps.org/supplemental/10.1103/ztxz-dwhk for the sample preparation, chemical analysis, and molecular structure parameters, angular momenta and total energies of thorium fluoride cations.
  50. C. Zülch, K. Gaul, and R. Berger, Fundamental physics with the thermodynamically stable diatomic trication UF3+, Isr. J. Chem. 63, e202300035 (2023).
  51. C. Zülch, K. Gaul, and R. Berger (unpublished).
  52. K. Gaul and R. Berger, Toolbox approach for quasi-relativistic calculation of molecular properties for precision tests of fundamental physics, J. Chem. Phys. 152, 044101 (2020).
  53. C. van Wüllen, A quasirelativistic two-component density functional and Hartree-Fock program, Z. Phys. Chem 224, 413 (2010).
  54. R. Ahlrichs, M. Bär, M. Häser, H. Horn, and C. Kölmel, Electronic structure calculations on workstation computers: The program system turbomole, Chem. Phys. Lett. 162, 165 (1989).
  55. J. P. Perdew, K. Burke, and M. Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett. 77, 3865 (1996).
  56. Y. A. Bernard, Y. Shao, and A. I. Krylov, General formulation of spin-flip time-dependent density functional theory using non-collinear kernels: Theory, implementation, and benchmarks, J. Chem. Phys. 136, 204103 (2012).
  57. C. van Wüllen, Molecular density functional calculations in the regular relativistic approximation: Method, application to coinage metal diatomics, hydrides, fluorides and chlorides, and comparison with first-order relativistic calculations, J. Chem. Phys. 109, 392 (1998).
  58. W. Liu, C. van Wüllen, F. Wang, and L. Li, Spectroscopic constants of MH and M2 (M = Tl, E113, Bi, E115): direct comparisons of four- and two-component approaches in the framework of relativistic density functional theory, J. Chem. Phys. 116, 3626 (2002).
  59. K. G. Dyall, Relativistic and nonrelativistic finite nucleus optimized triple-zeta basis sets for the 4p, 5p and 6p elements, Theor. Chem. Acc. 108, 335 (2002).
  60. K. G. Dyall, Relativistic quadruple-zeta and revised triple-zeta and double-zeta basis sets for the 4p, 5p, and 6p elements, Theor. Chem. Acc. 115, 441 (2006).
  61. L. Visscher and K. G. Dyall, Dirac-Fock atomic electronic structure calculations using different nuclear charge distributions, At. Data Nucl. Data Tables 67, 207 (1997).
  62. A. Mathew, G. B. Eijkel, I. G. M. Anthony, S. R. Ellis, and R. M. A. Heeren, Characterization of microchannel plate detector response for the detection of native multiply charged high mass single ions in orthogonal-time-of-flight mass spectrometry using a Timepix detector, J. Mass Spectrom. 57, e4820 (2022).
  63. A. A. J. Wei, A. Joshi, Y. Chen, and J. S. McIndoe, Strategies for avoiding saturation effects in ESI-MS, Int. J. Mass Spectrom. 450, 116306 (2020).
  64. A. Kramida and Y. Ralchenko, Atomic Spectra Database, NIST Standard Reference Database 78, https://www.nist.gov/pml/atomic-spectra-database (NIST, Gaithersburg, 1999).
  65. D. Schröder and H. Schwarz, Generation, stability, and reactivity of small, multiply charged ions in the gas phase, J. Chem. Phys. A 103, 7385 (1999).
  66. K. Franzreb, J. Hrusak, M. E. Alikhani, J. Lörincik, R. C. Sobers, and P. Williams, Gas-phase diatomic trications of Se23+, Te23+, and LaF3+, J. Chem. Phys. 121, 12293 (2004).
  67. J. Ladislas Wiza, Microchannel plate detectors, Nucl. Instrum. Methods 162, 587 (1979).
  68. B. Brehm, J. Grosser, T. Ruscheinski, and M. Zimmer, Absolute detection efficiencies of a microchannel plate detector for ions, Meas. Sci. Technol. 6, 953 (1995).
  69. G. Fraser, The ion detection efficiency of microchannel plates (MCPs), Int. J. Mass Spectrom. 215, 13 (2002).

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Phys. Rev. A 112, 012821– Published 24 July, 2025
  • Received 21 February 2025
  • Accepted 9 June 2025
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