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arXiv:physics/9703011 · Physical Review A

Photodetachment study of the 1s3s4s4S resonance in He −

Andreas E. Klinkmüller, G. Haeffler, D. Hanstorp, Igor Yu. Kiyan, Uldis Berzinsh, Christopher W. Ingram, D. J. Pegg, James R. Peterson

Published Oct 1, 1997• 15 citations
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Abstract

A Feshbach resonance associated with the ${1s3s4s}^{4}S$ state of He${}^{\ensuremath{-}}$ has been observed in the He${(1s2s}^{3}S)$ + ${e}^{\ensuremath{-}}(\ensuremath{\epsilon}s)$ partial photodetachment cross section. The residual He${(1s2s}^{3}S)$ atoms were resonantly ionized and the resulting He${}^{+}$ ions were detected in the presence of a small background. A collinear laser-ion beam apparatus was used to attain both high resolution and sensitivity. We measured a resonance energy ${E}_{\mathrm{r}}=2.959255(7)$ eV and a width $\ensuremath{\Gamma}=0.19(3)$ meV, in agreement with a recent calculation.

DOI
10.1103/physreva.56.2788

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A Feshbach resonance associated with the 1s3s4s4S{1s3s4s}^{4}S1s3s4s4S state of He\ensuremath−{}^{\ensuremath{-}}\ensuremath− has been observed in the He(1s2s3S){(1s2s}^{3}S)(1s2s3S) + e\ensuremath−(\ensuremathϵs){e}^{\ensuremath{-}}(\ensuremath{\epsilon}s)e\ensuremath−(\ensuremathϵs) partial photodetachment cross section. The residual He(1s2s3S){(1s2s}^{3}S)(1s2s3S) atoms were resonantly ionized and the resulting He+{}^{+}+ ions were detected in the presence of a small background. A collinear laser-ion beam apparatus was used to attain both high resolution and sensitivity. We measured a resonance energy Er=2.959255(7){E}_{\mathrm{r}}=2.959255(7)Er​=2.959255(7) eV and a width \ensuremathΓ=0.19(3)\ensuremath{\Gamma}=0.19(3)\ensuremathΓ=0.19(3) meV, in agreement with a recent calculation.
The photodetachment cross section of has been measured in the photon energy range 2.9-3.3 eV in order to investigate doubly excited states. Measurements were made channel specific by selectively detecting the residual He atoms left in a particular excited state following detachment. Three Feshbach resonances were found in the partial cross section: a resonance below the threshold and two resonances below the threshold. The measured energies of these doubly excited states are 2.959 260(6), 3.072(7) and 3.264 87(5) eV. The corresponding widths are found to be 0.20(2), 50(5) and 0.61(5) meV. The measured energies agree well with recent theoretical predictions for the , and states, respectively, but the widths deviate noticeably from calculations for and states.
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
The negative ion of lanthanum, La–\mathrm{L}{\mathrm{a}}^{\text{--}}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–\mathrm{L}{\mathrm{a}}^{\text{--}}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–\mathrm{L}{\mathrm{a}}^{\text{--}}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–\mathrm{L}{\mathrm{a}}^{\text{--}}La– to both ground and excited states of La. The present results provide information on the excited state structure and dynamics of La–\mathrm{L}{\mathrm{a}}^{\text{--}}La– that depend crucially on multielectron correlation effects.
A collinear beam apparatus has been used to study photodetachment of Cs${}^{\ensuremath{-}}$. Partial cross sections were measured using state-selective detection based on a resonance ionization scheme. Several resonances were observed in the Cs(102S10{\phantom{\rule{0.16em}{0ex}}}^{2}S102S), Cs(62F6{\phantom{\rule{0.16em}{0ex}}}^{2}F62F), Cs(62G6{\phantom{\rule{0.16em}{0ex}}}^{2}G62G), and Cs(62H6{\phantom{\rule{0.16em}{0ex}}}^{2}H62H) final-state channels below the Cs(102P10{\phantom{\rule{0.16em}{0ex}}}^{2}P102P3/2{}_{3/2}3/2​) channel opening. A model was developed to account for the interference between overlapping resonances. This model is essentially a generalization of the Fano [U. Fano, Phys. Rev. 124, 1866 (1961)] and Shore [B. W. Shore, Phys. Rev. 171, 43 (1968)] parametrizations for single resonances. Resonance parameters were extracted by fitting the model to the data sets. The openings of the Cs(102S10{\phantom{\rule{0.16em}{0ex}}}^{2}S102S) and Cs(62F6{\phantom{\rule{0.16em}{0ex}}}^{2}F62F) channels, where the polarizabilities of the atomic states are large and positive, showed rapid onsets. In the case of the Cs(62G6{\phantom{\rule{0.16em}{0ex}}}^{2}G62G) and Cs(62H6{\phantom{\rule{0.16em}{0ex}}}^{2}H62H) channels, on the other hand, the photodetachment cross sections increased slowly with energy. For the Cs(62H6{\phantom{\rule{0.16em}{0ex}}}^{2}H62H) channel this is the expected behavior, since it is the result of a large and negative polarizability of the 62H6{\phantom{\rule{0.16em}{0ex}}}^{2}H62H state. In addition, the excitation of the Cs(62H6{\phantom{\rule{0.16em}{0ex}}}^{2}H62H) state with respect to the Cs ground state was found to be 28 356.3(2) ${\mathrm{cm}}^{\ensuremath{-}1}$, in agreement with a previous experiment.
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.
In a recent experiment, Lindahl et al. ( Lindahl A. O. et al. , Phys. Rev. Lett. , 108 (2012) 033004) observed a new threshold behavior in the photodetachment of the potassium negative ion when the residual atom is left in the state. Unfortunately the resonance close to threshold made it more difficult to apply the semi-classical model that was developed to describe the threshold behavior. In this paper we present a study of the threshold behavior of the partial cross-section in the photodetachment of the sodium negative ion. The experiment was conducted using a collinear beams apparatus where the detection was performed using a resonance ionization scheme. We observe the same threshold behavior as in the previous experiment, but without any obfuscating resonance. The model derived in the previous paper is found to fit the observed cross-section up to 35 meV above threshold. The present experiment clearly demonstrates the threshold behaviour for the fundamental process of a free electron moving in the field of an atom with a large negative polarizability.