Cold Hypersonic Gas Jets for Precision Laser Spectroscopy of Radioactive Molecules

Abstract

The sensitivity to possible beyond standard model physics via a study of the nuclear Schiff moment (NSM) has since recently been driving laser spectroscopy of short-lived radioactive molecules. These experiments have in part been hindered by inefficient cooling of the molecular degrees of freedom, resulting in complex, difficult to interpret molecular spectra. Hypersonic (de Laval) nozzles have been shown to provide ideal environments to study cold short-lived actinides by means of in-gas-jet laser ionization spectroscopy. We present here the first application of this technique on molecules using ^229,230,232ThO laser ablation targets. Translational and rotational temperatures were characterized via laser spectroscopy and found to be 12.5(25) K and 7.2(6) K, respectively, along the nozzle-collimated 60 mm-long, 5 mm-diameter gas jet. An upper bound of the vibrational temperature was estimated as no transitions from v''=1 were observed. Molecular King-plot analysis shows a large field shift of −4.0(13) cm⁻¹/fm², indicating enhanced sensitivity to the differential nuclear charge radii. Relativistic FSCCSD calculations reproduce the measured molecular field-shift factor, providing a benchmark between state-of-the-art molecular and atomic calculations.

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BibTeX RIS

BibTeX

@misc{claessens2026cold,
  title = {{Cold Hypersonic Gas Jets for Precision Laser Spectroscopy of Radioactive Molecules}},
  author = {A. Claessens and R. Ferrer and Harshithbabu and L. M. Arndt and Ch. E. Düllmann and K. Gaul and F. Ivandikov and G. Neyens and D. Renisch and J. Stricker and W. Saelens and P. Van den Bergh and P. Van Duppen},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.38242},
  eprint = {2610.38242},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.38242},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Cold Hypersonic Gas Jets for Precision Laser Spectroscopy of Radioactive Molecules
AU  - A. Claessens
AU  - R. Ferrer
AU  - Harshithbabu
AU  - L. M. Arndt
AU  - Ch. E. Düllmann
AU  - K. Gaul
AU  - F. Ivandikov
AU  - G. Neyens
AU  - D. Renisch
AU  - J. Stricker
AU  - W. Saelens
AU  - P. Van den Bergh
AU  - P. Van Duppen
PY  - 2026
DA  - 2026/10/28
PB  - arXiv
DO  - 10.48550/arxiv.2610.38242
UR  - https://arxiv.org/abs/2610.38242
AB  - The sensitivity to possible beyond standard model physics via a study of the nuclear Schiff moment (NSM) has since recently been driving laser spectroscopy of short-lived radioactive molecules. These experiments have in part been hindered by inefficient cooling of the molecular degrees of freedom, resulting in complex, difficult to interpret molecular spectra. Hypersonic (de Laval) nozzles have been shown to provide ideal environments to study cold short-lived actinides by means of in-gas-jet laser ionization spectroscopy. We present here the first application of this technique on molecules using ^229,230,232ThO laser ablation targets. Translational and rotational temperatures were characterized via laser spectroscopy and found to be 12.5(25) K and 7.2(6) K, respectively, along the nozzle-collimated 60 mm-long, 5 mm-diameter gas jet. An upper bound of the vibrational temperature was estimated as no transitions from v''=1 were observed. Molecular King-plot analysis shows a large field shift of −4.0(13) cm^−1/fm^2, indicating enhanced sensitivity to the differential nuclear charge radii. Relativistic FSCCSD calculations reproduce the measured molecular field-shift factor, providing a benchmark between state-of-the-art molecular and atomic calculations.
ER  -

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