Determination of the Interval between the Ground States of Para- and Ortho- H2

M. Beyer*, N. Hölsch, J. Hussels, C. F. Cheng, E. J. Salumbides, K. S.E. Eikema, W. Ubachs, Ch Jungen, F. Merkt

*Corresponding author for this work

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Nuclear-spin-symmetry conservation makes the observation of transitions between quantum states of ortho- and para-H2 extremely challenging. Consequently, the energy-level structure of H2 derived from experiment consists of two disjoint sets of level energies, one for para-H2 and the other for ortho-H2. We use a new measurement of the ionization energy of para-H2 [EI(H2)/(hc)=124 417.491 098(31) cm-1] to determine the energy separation [118.486 770(50) cm-1] between the ground states of para- and ortho-H2 and thus link the energy-level structure of the two nuclear-spin isomers of this fundamental molecule. Comparison with recent theoretical results [M. Puchalski et al., Phys. Rev. Lett. 122, 103003 (2019)PRLTAO0031-900710.1103/PhysRevLett.122.103003] enables the derivation of an upper bound of 1.5 MHz for a hypothetical global shift of the energy-level structure of ortho-H2 with respect to that of para-H2.

Original languageEnglish
Article number163002
Pages (from-to)1-6
Number of pages6
JournalPhysical Review Letters
Issue number16
Publication statusPublished - 16 Oct 2019


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