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Physical Review A

High-resolution measurement of the electron affinity of cesium

José E. Navarro Navarrete, Miranda Nichols, Annie Ringvall-Moberg, Jakob Welander, D. C. Lu, D. Leimbach, Moa K. Kristiansson, Gustav Eklund, Meena Raveesh, Ruslan V. Chulkov, Vitali Zhaunerchyk, D. Hanstorp

Published Feb 21, 2024• 4 citations
Publisher

Abstract

Negative ions are unique quantum systems where electron correlation plays a decisive role in determining their properties. The lack of optically allowed transitions prevents traditional optical spectroscopy and the electron affinity is, therefore, for most elements, the only atomic quantity that can be determined with high accuracy. In this work, we present a high-precision experimental determination of the electron affinity of cesium. A collinear laser-ion beam apparatus was used to investigate the partial photodetachment cross section for the cesium anion, leaving the neutral atom in the 6p 2P3/2 excited state. A resonance ionization scheme was used to obtain final-state selectivity, which enabled the investigation of a sharp onset of the cross section associated with a Wigner s -wave threshold behavior. The electron affinity was determined to be 0.4715983(38)eV . Published by the American Physical Society 2024

DOI
10.1103/physreva.109.022812

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Negative ions are unique quantum systems where electron correlation plays a decisive role in determining their properties. The lack of optically allowed transitions prevents traditional optical spectroscopy and the electron affinity is, therefore, for most elements, the only atomic quantity that can be determined with high accuracy. In this work, we present a high-precision experimental determination of the electron affinity of cesium. A collinear laser-ion beam apparatus was used to investigate the partial photodetachment cross section for the cesium anion, leaving the neutral atom in the 6p 2P3/2 excited state. A resonance ionization scheme was used to obtain final-state selectivity, which enabled the investigation of a sharp onset of the cross section associated with a Wigner s -wave threshold behavior. The electron affinity was determined to be 0.4715983(38)eV . Published by the American Physical Society 2024
We have investigated the threshold of photodetachment of ${\mathrm{Li}}^{\mathrm{\ensuremath{-}}}$ leading to the formation of the residual Li atom in the 2p2{\mathit{p}}^{2}p2P state. The excited residual atom was selectively photoionized via an intermediate Rydberg state and the resulting Li+{\mathrm{Li}}^{+}Li+ ion was detected. A collinear laser-ion beam geometry enabled both high resolution and sensitivity to be attained. We have demonstrated the potential of this state-selective photodetachment spectroscopic method by improving the accuracy of Li electron affinity measurements an order of magnitude. From a fit to the Wigner law in the threshold region, we obtained a Li electron affinity of 0.618 049(20) eV. \textcopyright{} 1996 The American Physical Society.
Abstract Negative ions, which are formed when an electron is attached to a neutral system, are unique quantum systems. The lack of a long-range Coulomb force causes the inter-electronic interactions to become relatively more important. As a consequence, the independent particle model, which adequately describes atomic structure under normal conditions, breaks down. The alkali negative ions, with a closed valence s-shell, are among the simplest anionic systems. Hence, they can favorably be used to benchmark atomic theory. In this work, we have determined the electron affinity of 85Rb by measuring the relative partial photodetachment cross section of the negative ion, leaving the residual atom in the 5p 2 P 3 / 2 excited state. Resonance ionization spectroscopy allows for state selectivity and the ability to measure the Wigner s-wave threshold onset of the photodetachment process. The electron affinity of 85Rb was determined to be 485.887(6) meV.
The negative ion of cerium is investigated experimentally with tunable infrared laser photodetachment spectroscopy and theoretically with relativistic configuration interaction in the continuum formalism. The relative cross section for neutral atom production is measured with a crossed ion-beam--laser-beam apparatus over the photon energy range of 0.54--0.75 eV. A rich resonance spectrum is revealed near the threshold with, at least, 12 peaks observed due to transitions from bound states of ${\mathrm{Ce}}^{\ensuremath{-}}$ to either bound or quasibound excited states of the negative ion. Theoretical calculations of the photodetachment cross sections enable identification of the transitions responsible for the measured peaks. Two of the peaks are due to electric dipole-allowed bound-bound transitions in ${\mathrm{Ce}}^{\ensuremath{-}}$, making cerium only the second atomic negative ion that has been demonstrated to support multiple bound states of opposite parity. In addition, combining the experimental data with the theoretical analysis determines the electron affinity of cerium to be 0.628(10) eV and the fine structure splitting of the ground state of ${\mathrm{Ce}}^{\ensuremath{-}}$ (4H7/2−−4H9/2{}^{4}\phantom{\rule{-0.16em}{0ex}}{H}_{7/2}--{}^{4}\phantom{\rule{-0.16em}{0ex}}{H}_{9/2}4H7/2​−−4H9/2​) to be 0.097 75(4) eV.
Atomic lanthanum anion ${\mathrm{La}}^{\ensuremath{-}}$ is the best candidate for laser cooling of any atomic anions found so far. The bound-bound electric dipole transitions of ${\mathrm{La}}^{\ensuremath{-}}$ have been identified and measured. Theoretical studies have shown that ${\mathrm{La}}^{\ensuremath{-}}$ has a very complicated electronic structure, which cannot be well resolved by the traditional photoelectron spectroscopy. In the present work, we report high-resolution photoelectron spectroscopy of ${\mathrm{La}}^{\ensuremath{-}}$ via the slow-electron velocity-map imaging method in combination with an ion trap. The electron affinity of La was determined to be $4496.97(20)\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ or 0.557 553(25) eV. In addition, the energy levels of ${\mathrm{La}}^{\ensuremath{-}}$, 3F3e^{3}F_{3}^{e}3F3e​, 3F4e^{3}F_{4}^{e}3F4e​, 1D2e^{1}D_{2}^{e}1D2e​, 1D2o^{1}D_{2}^{o}1D2o​, 3P0e^{3}P_{0}^{e}3P0e​, 3P1e^{3}P_{1}^{e}3P1e​, and 3P2e^{3}P_{2}^{e}3P2e​, were also determined.
Photodetachment spectroscopy is a powerful spectroscopic technique for determining the internal state distribution of a molecular anion. Previously, our group studied the threshold photodetachment spectroscopy of CN⁻ at both 16 Kelvin and 295 Kelvin in a 22-pole ion trap and measured the electron affinity of CN with great precision (EA: 3.864(2) eV). The dicarbon anion, our current molecule of interest, is a well-studied system due to its stable electronic level structure and potential laser cooling transition. Here we present the threshold photodetachment spectroscopy study of C₂⁻ in a radiofrequency 16-pole ion trap at 8 Kelvin. We investigated the behavior of the cross section near the threshold for the ground state transition, C₂X¹Σ⁺g ← C₂⁻ X²Σ⁺g. We see a p-wave behavior for this ground state detachment. And we measured the electron affinity, which is consistent with the previously measured values."