Single, double, and triple photoionization of Ne + ions by single photons have been investigated at the synchrotron radiation source PETRA III in Hamburg, Germany. Absolute cross-sections were measured by employing the photon-ion merged-beams technique. Photon energies were between about 840 and 930 eV, covering the range from the lowest-energy resonances associated with the excitation of one single K-shell electron up to double excitations involving one K-and one L-shell electron, well beyond the K-shell ionization threshold. Also, photoionization of neutral Ne was investigated just below the K edge. The chosen photon energy bandwidths were between 32 and 500 meV, facilitating the determination of natural line widths. The uncertainty of the energy scale is estimated to be 0.2 eV. For comparison with existing theoretical calculations, astrophysically relevant photoabsorption cross-sections were inferred by summing the measured partial ionization channels. Discussion of the observed resonances in the different final ionization channels reveals the presence of complex Auger-decay mechanisms. The ejection of three electrons from the lowest K-shell-excited Ne + ( s s p 1 2 2 S 2 6 2 1 2 ) level, for example, requires cooperative interaction of at least four electrons.

Abstract.The photon-ion merged-beams technique has been employed at the new PhotonIon spectrometer at PETRA III (PIPE) for measuring multiple photoionization of Xe Absolute cross sections for 3d photoionization of Xe q+ ions (1 ≤ q ≤ 5) 2

Single, double, and triple ionization of C(1+) ions by single photons is investigated in the energy range of 286-326 eV, i.e., in the range from the lowest-energy K-vacancy resonances to well beyond the K-shell ionization threshold. Clear signatures of C(1+)(1s2s(2)2p(2) (2)D,(2)P) resonances are found in the triple-ionization channel. The only possible mechanism producing C(4+)(1s(2)) via these resonances is direct triple-Auger decay, i.e., a four-electron process with simultaneous emission of three electrons.

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Abstract.A crossed-beams setup was used to measure cross sections for electron-impact single and double ionization of W 17+ ions. Absolute data and high-resolution scan spectra were obtained at collision energies ranging from threshold up to 1000 eV. Comparison of the experimental results with theoretical calculations for direct ionization suggests substantial contributions of excitation-autoionization processes to electron-impact single ionization of W 17+ .

We report on new measurements of m-fold photodetachment (m = 2 − 5) of carbon anions via K-shell excitation and ionization. The experiments were carried out employing the photon-ion merged-beams technique at a synchrotron light source. While previous measurements were restricted to double detachment (m = 2) and to just the lowest-energy K-shell resonance at about 282 eV, our absolute experimental m-fold detachment cross sections at photon energies of up to 1000 eV exhibit a wealth of new thresholds and resonances. We tentatively identify these features with the aid of detailed atomic-structure calculations. In particular, we find unambiguous evidence for fivefold detachment via double K-hole production.Atomic anions are highly correlated systems where the extra electron is weakly bound to an overall neutral charge distribution. Consequently, the number of excited states of atomic anions is quite limited [1] and some atomic species such as nitrogen do not form anions at all. A thorough treatment of the correlation effects in negative atomic ions still poses a formidable challenge to atomic theory, and this becomes even greater for innershell vacancies, since the valence electrons are then subject to strong many-electron relaxation effects following the creation of core holes [2, 3]. On the experimental side, core holes can be readily created by exciting or ionizing an inner-shell electron by a photon. For light ions, the core-hole state will subsequently decay via Auger transitions such that electrons are emitted with the net effect of photoionization. For negative ions, the entire process is termed (multiple) photodetachment.So far, photodetachment via the initial creation of a single K-hole has been experimentally studied only for a limited number of light anions up to F − [3-9]. For C − ions especially, previous measurements were carried out by Gibson et al. [7] and by Walter et al. [8] who studied double photodetachment in a very narrow photon energy range just covering the 1s 2 2s 2 2p 3 4 S → 1s 2s 2 2p 4 4 P resonance at about 282 eV. This scarcity of data is due to the fact that sufficiently high photon fluxes for more comprehensive studies were not available. Here, we present absolute cross sections, σ m , for m-fold photodetachment of C − ions by a single photon,with m = 2, 3, 4, 5 and photon energies from below the K-edge up to ∼1000 eV. These cross sections provide a view of the photodetachment dynamics of a highly correlated atomic system in unprecedented detail. Apart from the resonance at ∼282 eV, we observed a number of additional photodetachment resonances with a variety of line shapes as well as a clear signature for multiple detachment by direct double K-hole production. To better understand these observations, detailed atomic-structure calculations were performed by using the GRASP [10] and RATIP [11] codes as well as the Jena Atomic Calculator (JAC) [12]. To the best of our knowledge, there is only one other theoretical study of highly excited resonances in C − which, however, is focussed exc...

In a joint experimental and theoretical endeavour, photoionization of metastable C 4+ (1s2s 3 S1) ions via intermediate levels with hollow, double-K -vacancy configurations 2s2p, 2s3p, 2p3s, 2p3d, 2s4p, 2p4s and 2p4d has been investigated. High-resolution photon-ion merged-beams measurements were carried out with the resolving power reaching up to 25,000 which is sufficient to separate the leading fine-structure components of the 2s2p 3 P term. Many-body perturbation theory was employed to determine level-to-level cross sections for K -shell excitation with subsequent autoionization. The resonance energies were calculated with inclusion of electron correlation and radiative contributions. Their uncertainties are estimated to be below ±1 meV. Detailed balance confirms the present photoionization cross-section results by comparison with previous dielectronic-recombination measurements. The high accuracy of the theoretical transition energies together with the present experimental results qualify photoabsorption resonances in heliumlike ions as new, greatly improved energy-reference standards at synchrotron radiation facilities.

Single, double, and triple ionization of the C + ion by a single photon have been investigated in the energy range 286 to 326 eV around the K-shell single-ionization threshold at an unprecedented level of detail. At energy resolutions as low as 12 meV, corresponding to a resolving power of 24 000, natural linewidths of the most prominent resonances could be determined. From the measurement of absolute cross sections, oscillator strengths, Einstein coefficients, multi-electron Auger decay rates and other transition parameters of the main K-shell excitation and decay processes are derived. The cross sections are compared to results of previous theoretical calculations. Mixed levels of agreement are found despite the relatively simple atomic structure of the C + ion with only 5 electrons. This paper is a follow-up of a previous Letter [Müller et al., Phys. Rev. Lett. 114, 013002 (2015)].