AP-Seminare

Improved determination of the dissociation energy and ortho-para splitting of H2

by Joel Hussels (VU Amsterdam)

Europe/Berlin
Lecture Room KBW2.28 (GSI)

Lecture Room KBW2.28

GSI

Description
Recent QED calculations of the dissociation energy (D0) of H2 now approach accuracies similar as in simple atoms, making it an excellent benchmark quantity in quantum chemistry. New precision measurements of the GK-X transition, combined with other precise measurements, provide an order-of-magnitude improved value for D0. This transition is performed through Doppler-free two-photon spectroscopy using 179-nm radiation, generated by frequency up-conversion using a BBO and a special KBBF crystal. The fundamental pulses are the output of a chirp-compensated Ti:Sa oscillator-amplifier system seeded by a narrowband Ti:Sa cw laser at 716 nm, locked to a Cs clock standard via a frequency comb. This enables sub-MHz level of accuracies, giving an improvement to the 10−9 level of accuracy for D0 of both ortho- and para-H2. Invoking a direct transition between ortho- and para-H2+ ion, these results lead to the first direct determination of the para-ortho splitting in neutral H2. [1,2] The comparison of these accurate results with improved calculations provides a test of QED, and by extension the Standard Model of Physics. [1] C.-F. Cheng, J. Hussels, M. Niu, H.L. Bethlem , K.S.E. Eikema, E.J. Salumbides, W.M.G. Ubachs, M. Beyer, N. Hölsch, J.A. Agner, F. Merkt, L.-G. Tao, S.-M. Hu and Ch. Jungen, Phys. Rev. Lett. 121, 013001 (2018) [2] M. Beyer, N. Hölsch, J. Hussels, C.-F. Cheng, E.J. Salumbides, K.S.E. Eikema, W. Ubachs, Ch. Jungen and F. Merkt, Phys. Rev. Lett. 123, 163002 (2019)