Ionization and Dissociation Energies of Molecular Hydrogen
Abstract
Molecular hydrogen (H2) is the simplest neutral molecule and its ionization and dissociation energies are key benchmarks for testing first-principles calculations of nonadiabatic, relativistic, quantum-electrodynamic and finite-nuclear-size effects in molecules. To obtain improved H2 ionization and dissociation energies, we performed precision measurements of 15 transition frequencies in para-H2. They connect the X 1Σg+(v=0,N=0) ground state, the long-lived EF 1Σg+(v=0,N=0) excited state, and several high members of the np and nd Rydberg series with principal quantum number n in the range between 48 and 70. The new data by itself leads to a five times more accurate value of the ionization energy of the ground state of para-H2, equivalent to a relative frequency accuracy of 5× 10−11. Combined with a global network analysis of 45 energy intervals in para- and ortho-H2 that have been measured in the past three decades, we obtain new statistically robust values for the ionization energy [EI(0,0)/(hc)= 124 417.491 1573(58)~cm−1] and the dissociation energy [D0N=0=36 118.069 6646(58)~cm−1] of H2. These values have an unprecedented accuracy equivalent to 175 kHz. The network analysis also leads to improved term values and dissociation energies of the excited states involved in the analysis. By comparing the results with first-principles calculations of the level structures of H2 and H2+ , a significantly reduced upper bound of 540 kHz is derived for putative beyond-the-standard-model contributions to the energy difference between para- and ortho-H2.
Versions
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BibTeX
@misc{doran2026ionization,
title = {{Ionization and Dissociation Energies of Molecular Hydrogen}},
author = {Ioana Doran and Charlaine Roth and Nicolas Hölsch and Maximilian Beyer and Andrés Martínez de Velasco and Vincent Barbé and Mathieu Collombon and Elmer Gründeman and Julian J. Krauth and Jinjun Liu and Josef A. Agner and Urs Hollenstein and Andreas Osterwalder and Hansjürg Schmutz and Daniel Sprecher and Andrea Wüest and Wim Ubachs and Christian Jungen and Kjeld S. E. Eikema and Frédéric Merkt},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.40359},
eprint = {2610.40359},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.40359},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Ionization and Dissociation Energies of Molecular Hydrogen
AU - Ioana Doran
AU - Charlaine Roth
AU - Nicolas Hölsch
AU - Maximilian Beyer
AU - Andrés Martínez de Velasco
AU - Vincent Barbé
AU - Mathieu Collombon
AU - Elmer Gründeman
AU - Julian J. Krauth
AU - Jinjun Liu
AU - Josef A. Agner
AU - Urs Hollenstein
AU - Andreas Osterwalder
AU - Hansjürg Schmutz
AU - Daniel Sprecher
AU - Andrea Wüest
AU - Wim Ubachs
AU - Christian Jungen
AU - Kjeld S. E. Eikema
AU - Frédéric Merkt
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.40359
UR - https://arxiv.org/abs/2610.40359
AB - Molecular hydrogen (H_2) is the simplest neutral molecule and its ionization and dissociation energies are key benchmarks for testing first-principles calculations of nonadiabatic, relativistic, quantum-electrodynamic and finite-nuclear-size effects in molecules. To obtain improved H_2 ionization and dissociation energies, we performed precision measurements of 15 transition frequencies in para-H_2. They connect the X ^1Σ_g^+(v=0,N=0) ground state, the long-lived EF ^1Σ_g^+(v=0,N=0) excited state, and several high members of the np and nd Rydberg series with principal quantum number n in the range between 48 and 70. The new data by itself leads to a five times more accurate value of the ionization energy of the ground state of para-H_2, equivalent to a relative frequency accuracy of 5× 10^−11. Combined with a global network analysis of 45 energy intervals in para- and ortho-H_2 that have been measured in the past three decades, we obtain new statistically robust values for the ionization energy [E_I(0,0)/(hc)= 124 417.491 1573(58)~cm^−1] and the dissociation energy [D_0^N=0=36 118.069 6646(58)~cm^−1] of H_2. These values have an unprecedented accuracy equivalent to 175 kHz. The network analysis also leads to improved term values and dissociation energies of the excited states involved in the analysis. By comparing the results with first-principles calculations of the level structures of H_2 and H_2^+ , a significantly reduced upper bound of 540 kHz is derived for putative beyond-the-standard-model contributions to the energy difference between para- and ortho-H_2.
ER -