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Electron Affinity of the Carbon Dimer from Threshold Photodetachment Spectroscopy

Sruthi Purushu Melath1, Michael Hauck1, Christine Lochmann1, Robert Wild1, Timothy P. Softley2, Katrin Dulitz1, and Roland Wester1,*

  • *Contact author: roland.wester@uibk.ac.at
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Phys. Rev. Lett. 136, 223001 – Published 2 June, 2026

DOI: https://doi.org/10.1103/wvxs-6wz5

Abstract

Photodetachment spectroscopy of C2− anions across the thresholds to the two lowest electronic states of neutral C2 was carried out using rotationally cold trapped ions. The electron detachment was observed to follow p- and s-wave threshold behavior for transitions to the C2X1Σg+(v′=0) and C2a3Πu(v′=0) states, respectively, in agreement with the threshold laws derived by Wigner [Phys. Rev. 73, 1002 (1948)]. The ions were prepared at two different rotational temperatures, using a temperature-variable cryogenic 16-pole wire trap at 8 and 142 K, respectively. By fitting the two thresholds, an accurate value of the adiabatic electron affinity of C2 was determined as 26364.2±0.5  cm−1. The energy of the p-wave threshold was found to be particularly insensitive to rotational excitation, due to the absence of P- and R-branch excitations. The new electron affinity deviates significantly from a recent measurement using photoelectron spectroscopy [Laws et al. Nat. Commun. 10, 5199 (2019)].

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Phys. Rev. Lett. 136, 223001– Published 2 June, 2026
  • Received 21 October 2025
  • Revised 15 January 2026
  • Accepted 24 April 2026
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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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