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Controlling Isomer Population Using a Dual-Oscillator Infrared Free-Electron Laser

América Y. Torres-Boy*, Anoushka Ghosh, Myles B. T. Osenton, Akash C. Behera, Sandy Gewinner, Marco De Pas, Heinz Junkes, Wieland Schöllkopf, Alexander Paarmann et al.

Gert von Helden and Gerard Meijer†

  • *Contact author: torres@fhi.mpg.de
  • †Contact author: meijer@fhi.mpg.de
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Phys. Rev. Lett. 137, 013001 – Published 1 July, 2026

DOI: https://doi.org/10.1103/2hy7-w3qb

Abstract

We report on the control and characterization of the isomer population of ions inside superfluid helium nanodroplets, using two-color operation of a dual-oscillator infrared free-electron laser. The timing of both lasers is highly synchronized and their frequencies (or “colors”) can be tuned independently over a wide range. Interaction of the singly deuterated proton-bound dimer of dihydrogen phosphate and formate inside helium nanodroplets with both colors enables the control over its isomer population and the recording of—one-color hidden—infrared spectra of individual isomers.

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References (37)

  1. S. Arrhenius, Über die Reaktionsgeschwindigkeit bei der Inversion von Rohrzucker durch Säuren, Z. Phys. Chem. 4, 226 (1889).
  2. R. D. Levine, Molecular Reaction Dynamics (Cambridge University Press, Cambridge, England, 2005).
  3. B. C. Dian, A. Longarte, and T. S. Zwier, Conformational dynamics in a dipeptide after single-mode vibrational excitation, Science 296, 2369 (2002).
  4. E. M. Maçôas, L. Khriachtchev, M. Pettersson, J. Lundell, R. Fausto, and M. Räsänen, Infrared-induced conformational interconversion in carboxylic acids isolated in low-temperature rare-gas matrices, Vib. Spectrosc. 34, 73 (2004).
  5. G. E. Douberly, J. M. Merritt, and R. E. Miller, Infrared- infrared double resonance spectroscopy of the isomers of acetylene- HCN and cyanoacetylene- HCN in helium nanodroplets, J. Phys. Chem. A 111, 7282 (2007).
  6. B. C. Dian, G. G. Brown, K. O. Douglass, and B. H. Pate, Measuring picosecond isomerization kinetics via broadband microwave spectroscopy, Science 320, 924 (2008).
  7. J. R. Clarkson, E. Baquero, V. A. Shubert, E. M. Myshakin, K. D. Jordan, and T. S. Zwier, Laser-initiated shuttling of a water molecule between H-bonding sites, Science 307, 1443 (2005).
  8. A. Rana, P. A. Harville, T. Khuu, and M. A. Johnson, Microcanonical kinetics of water-mediated proton transfer in microhydrated 4-aminobenzoic acid, Science 389, 1143 (2025).
  9. A. Stamm, D. Maue, and M. Gerhards, Structural rearrangement by isomer-specific infrared excitation in the neutral isolated dihydrated cluster of 3-hydroxyflavone, J. Phys. Chem. Lett. 9, 4360 (2018).
  10. C. J. Moon, A. Min, and M. Y. Choi, Infrared-induced isomerization of invisible isomers (I5) using nanosecond laser spectroscopy, J. Phys. Chem. Lett. 17, 237 (2025).
  11. G. E. Douberly, J. M. Merritt, and R. E. Miller, IR–IR double resonance spectroscopy in helium nanodroplets: Photo-induced isomerization, Phys. Chem. Chem. Phys. 7, 463 (2005).
  12. C. M. Leavitt, A. B. Wolk, J. A. Fournier, M. Z. Kamrath, E. Garand, M. J. Van Stipdonk, and M. A. Johnson, Isomer-specific IR–IR double resonance spectroscopy of D2-tagged protonated dipeptides prepared in a cryogenic ion trap, J. Phys. Chem. Lett. 3, 1099 (2012).
  13. C. Seaiby, A. V. Zabuga, A. Svendsen, and T. R. Rizzo, IR-induced conformational isomerization of a helical peptide in a cold ion trap, J. Chem. Phys. 144, 014304 (2016).
  14. T. Khuu, A. Rana, S. C. Edington, N. Yang, A. B. McCoy, and M. A. Johnson, Observation of slow Eigen-Zundel interconversion in H+ (H2O)6 clusters upon isomer-selective vibrational excitation and buffer gas cooling in a cryogenic ion trap, J. Am. Soc. Mass Spectrom. 34, 737 (2023).
  15. A. Rana, P. A. Harville, T. Khuu, R. A. LaCour, T. Head-Gordon, and M. A. Johnson, The onset for vibrationally induced, intramolecular proton transfer at three water molecules in microhydrated 4-aminobenzoic acid, J. Phys. Chem. Lett. 16, 5252 (2025).
  16. J. Oomens, B. G. Sartakov, G. Meijer, and G. von Helden, Gas-phase infrared multiple photon dissociation spectroscopy of mass-selected molecular ions, Int. J. Mass Spectrom. 254, 1 (2006).
  17. N. C. Polfer and J. Oomens, Vibrational spectroscopy of bare and solvated ionic complexes of biological relevance, Mass Spectrom. Rev. 28, 468 (2009).
  18. A. I. G. Flórez, D.-S. Ahn, S. Gewinner, W. Schöllkopf, and G. von Helden, IR spectroscopy of protonated leu-enkephalin and its 18-crown-6 complex embedded in helium droplets, Phys. Chem. Chem. Phys. 17, 21902 (2015).
  19. L. Jašíková and J. Roithová, Infrared multiphoton dissociation spectroscopy with free-electron lasers: On the road from small molecules to biomolecules, Chem. Eur. J. 24, 3374 (2018).
  20. D. Jaroszynski, R. Prazeres, F. Glotin, and J. Ortega, Two-color free-electron laser operation, Phys. Rev. Lett. 72, 2387 (1994).
  21. R. Prazeres, F. Glotin, C. Insa, D. Jaroszynski, and J. Ortega, Two-colour operation of a free-electron laser and applications in the mid-infrared, Eur. Phys. J. D 3, 87 (1998).
  22. J. Ortega, Two-color experiments with infrared lasers, Nucl. Instrum. Methods Phys. Res., Sect. A 507, 8 (2003).
  23. H. Schwettman and T. Smith, Two-color free-electron laser driven by a radio-frequency linear accelerator, J. Opt. Soc. Am. B 6, 973 (1989).
  24. W. Schöllkopf, M. D. P. Sandy Gewinner, H. Junkes, W. Kirstaedter, W. B. Colson, D. H. Dowell, S. C. Gottschalk, J. W. Rathke, T. J. Schultheiss, A. M. M. Todd, L. M. Young, S. Kray, A. C. Behera, A. Y. Torres-Boy, M. Wolf, A. Paarmann, G. von Helden, and G. Meijer, A two-color dual-oscillator infrared free-electron laser, arXiv:2604.16189.
  25. A. Singh, S. Bergmeister, A. Azhagesan, P. Scheier, and A. F. Vilesov, Infrared spectroscopy of cations in helium nanodroplets, Rev. Sci. Instrum. 94, 093002 (2023).
  26. X. Zhang, N. B. Brauer, G. Berden, A. M. Rijs, and M. Drabbels, Mid-infrared spectroscopy of molecular ions in helium nanodroplets, J. Chem. Phys. 136, 044305 (2012).
  27. P. L. Raston and G. E. Douberly, Rovibrational spectroscopy of formaldehyde in helium nanodroplets, J. Mol. Spectrosc. 292, 15 (2013).
  28. D. Verma, R. M. P. Tanyag, S. M. O’Connell, and A. F. Vilesov, Infrared spectroscopy in superfluid helium droplets, Adv. Phys. X. 4, 1553569 (2019).
  29. A. Singh, A. Iguchi, T. C. Bernaards, Z. Golpariani, K. Mizuse, A. Fujii, H. Tanuma, T. Azuma, S. Kuma, and A. Vilesov, Infrared spectroscopy of radical cation clusters (NH3)2+ and (NH3)3+, J. Phys. Chem. A 129, 2472 (2025).
  30. K. K. Lehmann and G. Scoles, The ultimate spectroscopic matrix?, Science 279, 2065 (1998).
  31. J. P. Toennies and A. F. Vilesov, Superfluid helium droplets: A uniquely cold nanomatrix for molecules and molecular complexes, Angew. Chem., Int. Ed. 43, 2622 (2004).
  32. E. Mucha, A. I. González Flórez, M. Marianski, D. A. Thomas, W. Hoffmann, W. B. Struwe, H. S. Hahm, S. Gewinner, W. Schöllkopf, Seeberger, P. H, K. Pagel, and G. von Helden, Glycan fingerprinting via cold-ion infrared spectroscopy, Angew. Chem., Int. Ed. 56, 11248 (2017).
  33. D. A. Thomas, E. Mucha, M. Lettow, G. Meijer, M. Rossi, and G. von Helden, Characterization of a trans–trans carbonic acid–fluoride complex by infrared action spectroscopy in helium nanodroplets, J. Am. Chem. Soc. 141, 5815 (2019).
  34. A. Y. Torres-Boy, M. I. Taccone, C. Kirschbaum, K. Ober, T. Stein, G. Meijer, and G. von Helden, Investigation of the proton-bound dimer of dihydrogen phosphate and formate using infrared spectroscopy in helium droplets, J. Phys. Chem. A 128, 4456 (2024).
  35. See Supplemental Material at http://link.aps.org/supplemental/10.1103/2hy7-w3qb for the estimation of density of states of the isomers and complementary experimental data.
  36. D. D. Dlott and M. D. Fayer, Application of a two-color free-electron laser to condensed-matter molecular dynamics, J. Opt. Soc. Am. B 6, 977 (1989).
  37. J. P. Kraack, Ultrafast structural molecular dynamics investigated with 2D infrared spectroscopy methods, Top. Curr. Chem. 375, 113 (2017).

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Phys. Rev. Lett. 137, 013001– Published 1 July, 2026
  • Received 3 December 2025
  • Revised 20 March 2026
  • Accepted 12 May 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

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