Physical Chemistry, Short talk
PC-026

Cold chemistry of single trapped H2O+ ions with neutral HD molecules in a cryogenic ion trap

N. Sunil Kumar1, P. Paliwal1, M. Popov1, A. Li2, H. Guo3, S. Willitsch1*
1Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland, 2Key Laboratory of Synthetic and Natural Functional Molecule of the Ministry of Education, College of Chemistry and Materials Science, Northwest University, 710127 Xi’an, China, 3Department of Chemistry and Chemical Biology, Center for Computational Chemistry, University of New Mexico, Albuquerque, New Mexico 87131, USA

Precise quantum control of trapped molecules has emerged as a key technology in a wide range of applications such as precision spectroscopy, quantum computing, tests of fundamental physics, and state-to-state chemistry [1, 2, 3]. Trapped ions can also serve as an excellent platform for probing cold ion–neutral reactions, facilitating investigation at the low-temperature, low-density conditions characteristic of the interstellar medium (ISM).

In our recently developed cryogenic ion trap setup, we explored cold collisions between a single trapped H2O+ ion and cold HD molecules at a collision energy of 7 K. We demonstrated the isotope effect in this ion-neutral reaction by utilizing a single molecular ion, sympathetically cooled to a few millikelvin in a linear Paul trap, and non-destructively identifying its reaction products with the HD molecules. The experiments revealed a pronounced isotope effect at this low collision energy of 7 K, and were consistent with the computed values using the quasi-classical trajectories (QCT) method.

The current experimental setup is being developed with the primary goal of extending complex quantum logic spectroscopy (QLS) schemes to H2O+ ions. With the advancement in experimental techniques for the preparation, cooling, and coherent manipulation of molecular ions, precise quantum control of polyatomic molecular ions is feasible [2,4]. Such quantum control can open new prospects and allow state-selected chemistry studies in the future.

 

[1] M. Sinhal, Z. Meir, K. Najafian, G. Hegi, and S. Willitsch, Science (2020), 367(6483), 1213-1218.

[2] M. Sinhal and S. Willitsch p. 305 ff. in "Photonic Quantum Technologies: Science and Applications", ed. M. Benyoucef, Wiley-VCH (2023)

[3] G. D. Scholes, A. Olaya-Castro, S. Mukamel, A. Kirrander, K. K. Ni, G. J. Hedley, and N. L. Frank, The Journal of Physical Chemistry Letters (2025), 16(5), 1376-96.

[4] M. Deiß, S. Willitsch, and J. H. Denschlag. Nature Physics (2024), 20 (5), 713-721.