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Photodetachment spectroscopy of quasibound states of the negative ion of lanthanum

C. W. Walter, N. D. Gibson, N. B. Lyman, and J. Wang
Phys. Rev. A 102, 042812 – Published 13 October 2020
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  • INTRODUCTION
  • EXPERIMENTAL METHOD
  • RESULTS AND DISCUSSION
  • SUMMARY
  • ACKNOWLEDGMENTS
    • References

    Abstract

    The negative ion of lanthanum, La–, has one of the richest bound state spectra observed for an atomic negative ion and has been proposed as a promising candidate for laser-cooling applications. In the present experiments, La– was investigated using tunable infrared photodetachment spectroscopy. The relative signal for neutral atom production was measured with a crossed ion-beam–laser-beam apparatus over the photon energy range 585–920 meV (2120–1350 nm) to probe the continuum region above the La neutral atom ground state. Eleven prominent peaks were observed in the La– photodetachment cross section due to resonant excitation of quasibound transient negative ion states in the continuum, which subsequently autodetach. In addition, thresholds were observed for photodetachment from several bound states of La– to both ground and excited states of La. The present results provide information on the excited state structure and dynamics of La– that depend crucially on multielectron correlation effects.

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    • Received 12 August 2020
    • Accepted 16 September 2020

    DOI:https://doi.org/10.1103/PhysRevA.102.042812

    ©2020 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Electronic structure of atoms & moleculesElectronic transitionsPhotodetachment
    Atomic, Molecular & Optical

    Authors & Affiliations

    C. W. Walter*, N. D. Gibson, N. B. Lyman†, and J. Wang‡

    • Department of Physics and Astronomy, Denison University, Granville, Ohio 43023, USA

    • *walter@denison.edu.
    • †Present address: Boeing Satellite Systems, 1950 E Imperial Hwy, El Segundo, California 90245, USA
    • ‡Present address: Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA

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    Issue

    Vol. 102, Iss. 4 — October 2020

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    Images

    • Figure 1
      Figure 1

      Partial energy level diagram showing relevant states of La– and La. The excitation energies of La states are from Ref. [22] and the binding energies of bound states of La– are from Refs. [1, 11, 12]. The numbered arrows indicate assigned resonance transitions observed in the present study to the La– quasibound states A, B, C, and D (dashed lines).

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    • Figure 2
      Figure 2

      Measured neutral atom signal for photodetachment from La– showing 22 of the 23 observed resonance peaks (Peak 1 is near 260 meV). The data below 585 meV are from Walter et al. [1] and the data above 585 meV were acquired in the present study; the vertical scales of the two data sets are adjusted so that the neutral signals match up near their common boundary energy of 585 meV. The data over the entire range has been broadly binned (∼2–5 meV), and the narrow peaks are shown with finer bins. The solid line connects the data points to guide the eye. Relevant photodetachment thresholds from the four most strongly bound states of La– to low-lying states of neutral La are indicated by vertical bars.

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    • Figure 3
      Figure 3

      Photodetachment spectrum showing the threshold for La– (5d26s2F4e3) → La (5d26sF7/24) and a nearby resonance Peak 21; the solid line is a fit of a Wigner p-wave plus a Fano peak function. The arrow indicates the detachment threshold Et.

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    • Figure 4
      Figure 4

      Expanded view of two closely spaced resonances, Peaks 13 and 14, with Lorentzian fits.

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    • Figure 5
      Figure 5

      Measured photodetachment signals from La– over (a) Peak 15 and (b) Peak 19; with fits of the Fano resonance function [Eq. (2)]. These two peaks originate from transitions that have the same upper state but different lower states; their profiles are radically different due to the relative strengths of the resonant and continuum photodetachment channels for each transition. Whereas Peak 15 shows only a constructive contribution to the cross section due to the resonance, Peak 19 shows both destructive and constructive interference in the resonance-continuum interaction.

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