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Determination of the dissociation energy of para-H2
J. Hussels, C.-F.Cheng, K.S.E. Eikema, E.J. Salumbides, W. Ubachs, Department of Physics and Astronomy, VU Amsterdam; N.J. Hölsch, M. Beyer, F. Merkt, Laboratorium für Physikalische Chemie, ETH Zurich; S.-M. Hu, Hefei National Laboratory for Physical Science at the Microscale, USTC, C. Jungen, UCL, London
The dissociation energy (D0) of H2 is an excellent benchmark quantity in quantum chemistry, with recent QED calculations now approaching accuracies achievable in simple atoms. New precision measurements of the GK-X molecular transition, in combination with other precision measurements, recently provided a value for D0 in ortho-H2. [1] The GK-state is populated from the X-state through Doppler-free two-photon spectroscopy using 179-nm radiation, generated by frequency up-conversion using a BBO crystal and a KBBF crystal. The laser pulses at the fundamental wavelength are generated in a seeded, chirp-compensated, Ti:Sa oscillator-amplifier system where the seed is a narrowband Ti:Sa laser at 716 nm locked to a frequency comb. This enables sub-MHz level of accuracy for the GK-X energy splitting. In combination with CW-laser excitation of GK-np [2], millimeter wave transitions of inter-Rydberg transitions and extrapolation to the ionization limit, accurate values of the ionization limit and D0 of ortho-H2 were determined, the latter to 10−9 accuracy [1]. Here, additional work will be reported on para-H2, where the dissociation energy of the true ground state in the H2 molecule is determined. The difference of these two results gives the energy difference between the ground rovibronic states of ortho- and para-H2. The comparison of these accurate experimental results with improved calculations [3] may be interpreted to test the Standard Model of Physics [4].
[1] C.-F. Cheng, J. Hussels, M. Niu, H.L. Bethlem , K.S.E. Eikema, E.J. Salumbides, W. Ubachs, M. Beyer, N.J. Hölsch, J.A. Agner, F. Merkt, L.-G. Tao, S.-M. Hu and C. Jungen, PRL 121, 013001 (2018)
[2] M. Beyer, N. Hölsch, J. A. Agner, J. Deiglmayr, H.Schmutz, and F. Merkt,Phys. Rev. A97, 012501 (2018).
[3] M. Puchalski, J. Komasa, P. Czachorowski and K. Pachucki, Phys. Rev. Lett. 122, 103003 (2019)
[4] W. Ubachs, J.C.J. Koelemeij, K.S.E. Eikema and E.J. Salumbides, J. Mol. Spectr. 320, 1-12 (2016)