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Ionization energy of ${Rb}_{2}$ by electric field ionization of molecular Rydberg states

Manuel Alejandro Lefrán Torres ^*, David Rodríguez Fernández ^*, Jaime Javier Borges Márquez ^*, Marcos Roberto Cardoso , and Luis Gustavo Marcassa ^2,†

Amrendra Pandey ^*, Romain Vexiau , Olivier Dulieu , and Nadia Bouloufa-Maafa

Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil

Université Paris-Saclay, CNRS, Laboratoire Aimé Cotton, 91400 Orsay, France

^*These authors contributed equally to this work.
^†Contact author: marcassa@ifsc.usp.br

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Phys. Rev. Research 7, 043126 – Published 3 November, 2025

DOI: https://doi.org/10.1103/j8n4-j9kc

Abstract

We report the measurement of the ionization energy of the ${}^{85}{Rb}_{2}$ molecule through resonantly enhanced two-photon ionization in a supersonic beam. The first photon excites the $X^{1} Σ_{g}^{+} (v_{X} = 0) \to B^{1} Π_{u} (v_{B} = 2)$ transition, while the second photon wave number is scanned over the $16 730 - 16 755 {cm}^{- 1}$ range, thus yielding a structured spectrum of ${Rb}_{2}^{+}$ ions extracted by an electric field and recorded by mass spectrometry. We modeled the onset of the ionization signal as a function of the electric field strength between 18 and 180 V/cm, leading to the ${Rb}_{2}$ ionization energy $E_{i} = 31 497.3 \pm 0.6 {cm}^{- 1}$ and to the dissociation energy of the ${Rb}_{2}^{+}$ ground state $D_{0} = 6158.2 \pm 0.6 {cm}^{- 1}$ . Our measured value $E_{i}$ is found to be $149.3 {cm}^{- 1}$ larger than the one reported in the experiment by Bellos et al. [Phys. Rev. A 87, 012508 (2013)]. Our value of $D_{0}$ agrees with our theoretical determination using a quantum chemistry approach. Using a simple theoretical model, we assign unevenly spaced structures of the ionization spectrum to molecular Rydberg levels belonging to several series that converge to the lowest vibrational levels of ${Rb}_{2}^{+}$ .

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Atomic & molecular structure

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References (48)

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Phys. Rev. Research 7, 043126– Published 3 November, 2025

Vol. 7, Iss. 4 — November - December 2025

Received 14 July 2025
Accepted 11 September 2025

DOI: https://doi.org/10.1103/j8n4-j9kc

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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Ionization energy of ${Rb}_{2}$ by electric field ionization of molecular Rydberg states

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Ionization energy of Rb2 by electric field ionization of molecular Rydberg states

Abstract

Physics Subject Headings (PhySH)

Article Text

Supplemental Material

References (48)

Ionization energy of ${Rb}_{2}$ by electric field ionization of molecular Rydberg states