Extreme Correlation and Repulsive Interactions in Highly Excited Atomic Alkali Anions

Abstract

At high energies, single-photon photodetachment of alkali negative ions populates final states where both the ejected electron and the residual valence electron possess high angular momenta. The photodetached electron interacts strongly with the anisotropic core, and thus the partial cross sections for these channels display non-Wigner threshold behavior reflecting these large, and occasionally repulsive, interactions. Our fully quantum mechanical theoretical study enables a deeper interpretation of these partial cross sections. Comparisons of the behavior in different channels and between different atomic species -sodium, potassium, and cesium -show the critical role of near-degeneracies in the energy spectrum and demonstrate that much of the behavior of the partial photodetachment cross sections stems from the permanent, rather than induced, electric dipole moments of these nearly-degenerate channels. This provides a concrete example of a system where negative dispersion forces play a decisive role.Atomic negative ions are fertile sources of information about correlated electron behavior, shape and Fano-Feshbach resonances, and near-threshold behavior [1,2]. Negative ions of alkali atoms have an electron affinity around 0.5 eV [3,4] and possess only one weakly bound state [5]. At higher energies a rich spectrum of rapidly autodetaching doubly excited states appears [6][7][8][9][10]. Much of the interest in negative ions stems from the fact that, unlike positive ions or neutral systems, they are bound together not by the Coulomb potential but instead by far weaker polarization potentials which reveal subtle correlation effects. Furthermore, the alkali anions focussed on here are effective two-electron systems and thus are theoretically tractable to high accuracy [11][12][13].In the absence of dominant Coulomb forces, the structure of anions is determined by polarization potentials between the induced dipole moments of the extended electronic states and the additional electron [11]. These potentials cause the observed partial cross sections (PCSs) to deviate from the Wigner threshold law (TL), σ ∝ E l+1/2 e , where E e and l are the photoelectron's energy and angular momentum [14]. This was first noticed in photodetachment experiments of alkali anions just above the first excited threshold, where the relevant ground state polarizabilities α p are a few hundred atomic units and the Wigner TL fails surprisingly rapidly [15,16]; this sparked the development of several improved theoretical descriptions [11,12,[17][18][19][20]. These polarizabilities increase rapidly with the principal quantum number n, approximately as n 7 ; for states with n ≈ 6 and having large angular momenta, l max ≈ n − 1, α p ≈ 10 4 − 10 6 atomic units. At sufficiently high n and maximal l, α p can become negative, leading to an entirely repulsive potential [21].These long-range induced dipole potentials typically dominate the low energy photodetachment spectrum of alkali anions. H − is exceptional owing to its "accidental" degeneracy. The dege...

Formation of long-range Rydberg molecules in two-component ultracold gases

“…1 and standing wave scattering boundary conditions. Since many references extensively discuss this method and its use in such diverse applications as Rydberg photoionization, negative ion photodetachment, and electron scattering [48,[51][52][53][54][55], here the description focuses on the specific numerical implementation. We varied the size of the R-matrix region from 25a 0 to 55a 0 , distances large enough to contain a few low lying wave functions and also to ensure that the long-range potential outside of the R-matrix region is dominated by centrifugal and polarization contributions.…”

Predicting quasibound states of negative ions

“…3, together with a fit of the Fano resonance formula [34] with a linear background continuum cross section. The Fano profile provides an excellent fit to the data, yielding a resonance energy of 930.5 (9) meV and peak width of 5.8 (10) meV.…”

“…Laser cooling of negative ions may allow a sympathetic cooling of antiprotons for the production of cold antihydrogen for tests of fundamental symmetries [5,6]. From a fundamental standpoint, since the extra electron in a negative ion is not bound by a net Coulomb force, their properties critically depend on electron-electron correlation and polarization, giving valuable opportunities to gain insight into these important multibody interactions [7][8][9]. Therefore, negative ions serve as key test systems for state-of-the art atomic structure calculations.…”

Determination of the dipole polarizability of the alkali-metal negative ions

“…Electron affinities (EAs) of these systems have been measured very precisely [3][4][5][6][7]. Photoabsorption spectra of these ions have also been extensively investigated both theoretically and experimentally, in order to understand their structures [8][9][10][11]. Starting from seventies, a series of studies on the photodetachment of negative lithium (Li − ), sodium (Na − ) and potassium (K − ) ions have been conducted by several groups [5,[12][13][14][15].…”