Speaker
Description
The hydrogen molecule (H$_2$), as the smallest molecule, is the benchmark system for testing quantum electrodynamics calculations in molecular systems. In particular the values of the dissociation and ionization energies, linked to each other via a thermodynamic cycle, have been a target to compare theory with the most advanced experiments. Since the advent of quantum mechanics many orders of magnitude have been gained on both sides [1]. The Zurich-Amsterdam collaboration has made great progress in the past two decades gaining some two orders of magnitude in accuracy [2,3]. These results are in perfect agreement with state-of-the-art computations [4]. We will report a further improved experimental value of the ionization and dissociation limits at an accuracy of about 200 kHz [5].
A second target is the vibrational splitting, measured via a (2-0) overtone quadrupole transition for which an accurate value was reported [6]. In the latter studies it was found that in the saturation experiments of a very weak transition only a single recoil component is obtained. Recent trapping experiments show that indeed only a blue-shifted recoil component is observed, yielding an unambiguous value for the zero-recoil quantum vibrational level separation in the H$_2$ molecule at 8 kHz accuracy [7].
[1] D. Sprecher, Ch. Jungen, W. Ubachs, F. Merkt, Faraday Disc. 150, 51-70 (2011).
[2] J. Liu, E.J. Salumbides, U. Hollenstein, J.C.J. Koelemeij, K.S.E. Eikema, W. Ubachs, F. Merkt, J. Chem. Phys. 130, 174306 (2009).
[3] N. Hoelsch, M. Beyer, E.J. Salumbides, K.S.E. Eikema, W. Ubachs, C. Jungen, F. Merkt, Phys. Rev. Lett. 122, 103002 (2019).
[4] M. Puchalski, J. Komasa, P. Czachorowski, and K. Pachucki, Phys. Rev. Lett. 122, 103003 (2019).
[5] I. Doran, C. Roth, M. Beyer, W. Ubachs, K.S.E. Eikema, F. Merkt, et al., to be published (2026).
[6] F.M.J. Cozijn, M.L. Diouf, W. Ubachs, Phys. Rev. Lett. 131, 073001 (2023).
[7] W. Ubachs, F.M.J. Cozijn, M.L. Diouf, C. Lauzin, H. Jozwiak, P. Wcislo, Phys. Rev. Lett. 135, 223201 (2025).