Resonant triple-differential cross-section measurements on atomic strontium

Sheridan, Paul; Grimm, Matthias; Sokell, Emma

doi:10.1088/0953-4075/41/16/165204

Cited by 6 publications

(9 citation statements)

References 24 publications

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“…1) one sees that both the resonant and nonresonant CCC calculations clearly produce four lobes in the TDCS and they are well represented by a di-Gaussian amplitude. Thus these results prove that the extra lobes with respect to the He 1s observed in previous measurements on alkaline-earth-metal atoms [23][24][25][26] are produced by the structure of the initial state ns wave function. The resonant intermediate state only enhances their intensity.…”

supporting

confidence: 84%

“…While, on one hand, the resonance enhances the photoabsorption cross section, on the other hand, it may affect the shape of the TDCS. Indeed the observation of extra features in previous measurements of the TDCS of alkaline-earth-metal atoms [23][24][25][26] with respect to He was interpreted as a signature of an indirect process, where the DPI proceeds via an intermediate neutral excited state.…”

mentioning

confidence: 98%

“…The measurement of the TDCS of metal vapors even at the third generation synchrotron radiation sources is very challenging. Apart from one case in Ca [22], all the other measurements of the TDCS in alkaline-earth-metal atoms [23][24][25][26] have been made at energies corresponding to np ! n 0 d resonances in the double continuum.…”

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confidence: 99%

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Signature of Two-Electron Interference in Angular Resolved Double Photoionization of Mg

et al. 2013

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The double photoionization of Mg has been studied experimentally and theoretically in a kinematic where the two photoelectrons equally share the excess energy. The observation of a symmetrized gerade amplitude, which strongly deviates from the Gaussian ansatz, is explained by a two-electron interference predicted theoretically, but never before observed experimentally. Similar to the Cooper minima in the single photoionization cross section, the effect finds its origin in the radial extent and oscillation of the target wave function. DOI: 10.1103/PhysRevLett.110.083001 PACS numbers: 32.80.Fb The effect of the target orbital on the photoionization cross section in the form of the Cooper minimum has long been established [1] and commonly used to obtain information on the electronic structure in the gas phase [2] as well as in condensed matter [3,4]. The Cooper minimum, observed for all the orbitals with a number of nodes n À ' À 1 > 0, is determined by the vanishing radial overlap between the photoelectron wave function and the target orbital. Generally there are the two photoionization channels with photoelectron angular momenta ' AE 1, the node in the stronger channel is offset by a nonvanishing contribution in the weaker channel. The situation is much more complicated in double photoionization (DPI) where there are no simple bounds on the individual photoelectron angular momenta ' 1 and ' 2 other than coupling to the total angular momentum of the pair, and a large number of radial integrals contribute to the total integrated photoionization cross section. Hence, there is no simple analogue of the Cooper minimum in DPI.Nevertheless, a strong effect of the target electronic structure was observed in calculations of the angular correlation pattern in the two-electron continuum [5]. It has been shown that (i) for a given symmetry of the electron pair the angular correlation of DPI mimics the angular distribution of an e-impact ionization of the corresponding ion and (ii) the amplitudes of these processes are strongly determined by the radial extent and oscillations of the target orbital of the singly charged ion. In the case of the Cooper minimum, the contributions of the positive and negative oscillations of the target orbital cancel each other in the real and scalar quantity (the dipole radial integral). In the case of DPI, these contributions add up as complex and angular dependent amplitudes. They do not vanish entirely, but display an intricate interference pattern.For a long time, investigation of DPI was focused on the He atom, the simplest two-electron system [6][7][8]. Because of a nodeless 1s target orbital, the dynamic DPI amplitude of this process (also known as correlation factor [9]) showed a very simple Gaussian shape. Alkaline-earth-metal atoms (Be, Mg, Ca, Sr) are ''quasi-two-electron'' systems with the outermost orbitals characterized by one or more nodes and represent the most suitable candidates for extending the investigation of DPI beyond He. The theoretical DPI cross section of Be and hea...

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Signature of Two-Electron Interference in Angular Resolved Double Photoionization of Mg

et al. 2013

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“…This is in contrast with the single pair observed in the TDCS of He. In the case of Sr, the TDCS measured by West et al [20] and Sheridan et al [21] in the region of the 4p→4d resonance showed a nonzero value for antiparallel ejection of the two electrons (θ 12 = 180°). This particular kinematics cannot be accessed with our present setup, thus we have performed here a simulation and analysis of the TDCS that can be expected on the grounds of the experimental and theoretical results presented in the previous sections.…”

Section: Tdcs With θ 1 = 90°tmentioning

confidence: 89%

“…Thus, even at third-generation synchrotron radiation sources, the measurement of the TDCS is challenging and, to our knowledge, only a single TDCS in Ca has been reported in the nonresonant condition at an excess energy of 25 eV [17]. However, the presence of np → n d resonances in the double continuum has made possible the measurement of the TDCS in a few other cases [18][19][20][21]. While these resonances enhance the photoabsorption cross section and therefore the emission of the two electrons, they may affect the shape of the TDCS because the intermediate excited state populates the double continuum via the ejection of two electrons [22].…”

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confidence: 99%

Photo-double-ionization of Mg studied by electron-electron-coincidence experiments

et al. 2014

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The photo-double-ionization (PDI) of Mg to the Mg 2+ (3s −2) state has been studied by photoelectronphotoelectron-coincidence experiments at a photon energy corresponding to the excitation of the 2p→3d resonance. The equal energy sharing (E 1 = E 2 = 16.4 eV) as well as the complementary unequal energy (E 1 ↔E 2 = 10.4↔22.4 eV) sharing kinematics have been investigated. From the experimental results without any approximation the symmetrized gerade and ungerade amplitudes have been obtained. The experimental angular correlation patterns as well as the amplitudes are compared to CCC calculations in which the resonant process has been incorporated. The results confirm that the amplitudes of the photo-double-ionization carry the signature of the target radial wave function. The investigation of the triple differential cross sections has been then extended by simulations to a kinematics with the fixed detector at 90 o , which can not be studied experimentally by the present setup. These simulations shed light on results of previous measurements on alkaline-earth-metal atoms in this kinematics, which were not consistent with the common understanding of photo-double-ionization derived from He experiments.

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Photoion-yield study of the 3p–3d giant resonance excitation region of isolated Cr, Mn and Fe atoms

Osawa

Kawajiri

Suzuki

et al. 2012

J. Phys. B: At. Mol. Opt. Phys.

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Using the charge-separated photoion-yield method combined with monochromatized synchrotron radiation, single (M+) and double (M2+) photoionization spectra in the 3p excitation region were observed for isolated atoms M = Cr, Mn and Fe. The relaxation processes of excited states to double ionization, as well as to single ionization, were considered with the help of existing photoabsorption and photoelectron data and some calculations of highly-excited states of M+ using the atomic code GRASP92. In the 3p→3d giant resonance region before the 3p→n(s, d) Rydberg series starts, the spectral features in the M2+ channel are similar to those in the M+ channel. The ratios M2+/M+ in this region are rather constant accordingly against the photon energy with values 0.045 ± 0.005 for Cr, 0.17 ± 0.03 for Mn and 0.30 ± 0.08 for Fe at the giant resonance. The increase in the M2+/M+ ratio with increasing the atomic number Z can be explained by the increasing contribution of two-step double ionization via highly-excited M+ states. It is expected that, at the 3p→3d giant resonance, the one-step double ionization process occurs within a few per cent of the entire decay.

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Resonant triple-differential cross-section measurements on atomic strontium

Cited by 6 publications

References 24 publications

Signature of Two-Electron Interference in Angular Resolved Double Photoionization of Mg

Signature of Two-Electron Interference in Angular Resolved Double Photoionization of Mg

Photo-double-ionization of Mg studied by electron-electron-coincidence experiments

Photoion-yield study of the 3p–3d giant resonance excitation region of isolated Cr, Mn and Fe atoms

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