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Journal of Physics Conference Series

Accurate electron affinity of lanthanum atom

Yuzhu Lu, Rulin Tang, Xiaoxi Fu, Chuangang Ning

Published Jan 1, 2020• 0 citations
Publisher

Abstract

Synopsis Atomic lanthanum anion La− is the best candidate for laser cooling of any atomic anions by far. The previous theoretical studies showed that La− has very a complicated electronic structure, which cannot be well resolved by the traditional photoelectron spectroscopy. In the present work, we used the slow-electron velocity-map imaging method in combination with an ion trap to measure the electronic structure of La−. The electron affinity of La is accurately determined to be 4496.97(20) cm−1 or 0.557553(25) eV.

DOI
10.1088/1742-6596/1412/13/132026

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Physical Review A•Jun 1, 2016•10 citations
Synopsis Atomic lanthanum anion La− is the best candidate for laser cooling of any atomic anions by far. The previous theoretical studies showed that La− has very a complicated electronic structure, which cannot be well resolved by the traditional photoelectron spectroscopy. In the present work, we used the slow-electron velocity-map imaging method in combination with an ion trap to measure the electronic structure of La−. The electron affinity of La is accurately determined to be 4496.97(20) cm−1 or 0.557553(25) 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.
Despite the tremendous advances in laser cooling of neutral atoms and positive ions, no negatively charged ion has been directly laser cooled. The negative ion of lanthanum, La(-), has been proposed as the best candidate for laser cooling of any atomic anion [ and , Phys. Rev. A 81, 032503 (2010)]. Tunable infrared laser photodetachment spectroscopy is used to measure the bound-state structure of La(-), revealing a spectrum of unprecedented richness with multiple bound-bound electric dipole transitions. The potential laser-cooling transition ((3)F(2)(e)→(3)D(1)(o)) is identified and its excitation energy is measured. The results confirm that La^{-} is a very promising negative ion for laser-cooling applications.
High-resolution photoelectron energy spectra of osmium anions are obtained using the slow-electron velocity-map imaging method. The energy levels of excited states 4 F 7/2, 4 F 5/2 and 4 F 3/2 of Os− are determined to be 148.730(13), 155.69(15), and 176.76(13) THz [or 4961.09(41), 5193.4(49), and 5896.1(42) cm−1], respectively. The lifetime of the opposite-parity excited state 6 D 9 / 2 o is determined to be 201(10) μs using a cold ion trap, about 15 times shorter than the previous result 3(1) ms. Our high-level multi-configuration Dirac–Hartree–Fock calculations yield a theoretical lifetime 527 μs. Our work shows that the laser cooling rate of Os− is as fast as that of Th−. The advantages of Os− are its near-IR range cooling transition and simple electronic structure, which make Os− a promising candidate for laser cooling of negative ions. We propose a general approach to produce cold atoms and molecules based on the sympathetic cooling of negative ions in combination with a threshold photodetachment.
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
This study reinterprets an earlier experimental photoelectron kinetic energy spectrum of the negative ion of lanthanum [A. M. Covington, D. Calabrese, J. S. Thompson, and T. J. Kvale, J. Phys. B 31, L855 (1998)] by carrying out relativistic configuration interaction (RCI) photodetachment calculations. The results confirm the earlier RCI calculation for the electron affinity of lanthanum (0.545 eV) [S. M. O'Malley and D. R. Beck, Phys. Rev. A 79, 012511 (2009)] and revise it to a slightly larger value of 0.550 eV, thus modifying the experimental interpretation of $0.47\ifmmode\pm\else\textpm\fi{}0.02$ eV. The calculation also yields the binding energies of the other thirteen bound states of ${\mathrm{La}}^{\ensuremath{-}}$. Good agreement has been found when these energies are compared to the results of a recent experimental study on ${\mathrm{La}}^{\ensuremath{-}}$ [C. W. Walter, N. D. Gibson, D. J. Matyas, C. T. Crocker, K. A. Dungan, B. R. Matola, and J. Rohl\'en, Phys. Rev. Lett. 113, 063001 (2014)]. Finally, our analysis confirms the transition energy for the potential laser cooling transition of ${}^{3}{F}_{2}^{e}\ensuremath{\rightarrow}{}^{3}{D}_{1}^{o}$ in ${\mathrm{La}}^{\ensuremath{-}}$.