Absolute cross sections for photoionization of Xeq +ions (1 ⩽ q ⩽ 5) at the 3d ionization threshold (original) (raw)
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Absolute measurements of photoionization cross-sections for ions
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2005
A merged-beam setup for absolute measurements of photoionization cross-sections of ions is described. The facility is capable of recording cross-sections as low as 10 À19 cm 2 and has been used to study a large number of singly-and multiply-charged, atomic and molecular, positive and negative ions. It is based on a synchrotron radiation beam line fitted with an undulator at the storage ring ASTRID and a low-energy ($2 keV) ion beam line. Photons in the energy range 15-200 eV are merged co-linearly with the target ions over a distance of 50 cm, and the absolute photoionization cross-section is determined from the resulting photoion yield with a typical accuracy of 10%. Different types of ion sources are available, thus permitting a large number of positive and negative, atomic and molecular, singly-and multiply-charged ions to be investigated. Emphasis is put on accurate determination of the absolute cross-sections, requiring calibration of photodiode and particle detectors together with measurements of the photon-ion overlap.
Applied Sciences
In this work, we present the photon energy dependence of the two-and three-photon cross sections of the two-electron Li + , Ne 8+ and Ar 16+ ions, following photoionization from their ground state. The expressions for the cross sections are based on the lowest-order (non-vanishing) perturbation theory for the electric field, while the calculations are made with the use of an ab initio configuration interaction method. The ionization cross section is dominated by pronounced single photon resonances in addition to peaks associated with doubly excited resonances. In the case of two-photon ionization, and in the non-resonant part of the cross section, we find that the 1 D ionization channel overwhelms the 1 S one. We also observe that, as one moves from the lowest atomic number ion, namely Li + , to the highest atomic number ion, namely Ar 16+ , the cross sections generally decrease.
Photoionization of Astrophysically Relevant Atomic Ions at PIPE
We review recent work on the photoionization of atomic ions of astrophysical interest that has been carried out at the photon-ion merged-beams setup PIPE, a permanently installed end station at the XUV beamline P04 of the PETRA III synchrotron radiation source operated by DESY in Hamburg, Germany. Our results on single and multiple L-shell photoionization of Fe + , Fe 2+ , and Fe 3+ ions, and on single and multiple K-shell photoionization of C − , C + , C 4+ , Ne + , and Si 2+ ions are discussed in astrophysical contexts. Moreover, these experimental results bear witness of the fact that the implementation of the photon-ion merged-beams method at one of the world's brightest synchrotron light sources has led to a breakthrough for the experimental study of atomic inner-shell photoionization processes with ions. Atoms 2020, 8, 45 2 of 17 for U 91+ . Thus, photon energies from the vacuum ultraviolet (VUV) to the hard X-ray bands are needed for investigating photoionization of ions across the entire periodic table. Powerful laboratory sources for these types of radiation are hot plasmas and synchrotron light sources, which both have been used for photoabsorption and photoionization studies with atomic ions. The dual laser plasma (DLP) technique [12] uses a laser-generated hot plasma as a back-lighter for absorption measurements with ions in a second laser-generated plasma. In contrast to the broad spectral distribution of the radiation from a hot plasma, synchrotron radiation has a much narrower photon-energy bandwidth and it is freely tunable over large energy ranges. Moreover, modern third generation synchrotron light sources provide a high photon flux, which is a prime necessity for experiments with dilute targets, such as ions, whose mutual electrostatic repulsion entails low particle densities. The density of ionic targets can be increased in ion traps, where the ion cloud can be compressed by external fields and its density can be increased by applying cooling techniques. Nevertheless, the signal rates from such arrangements are usually still rather low and, therefore, photoionization of trapped atomic ions has been performed in only a few cases , so far.
Physical Review A, 2006
Absolute photoionization cross-section measurements for a mixture of ground and metastable states of Xe 4+ , Xe 5+ , and Xe 6+ are reported in the photon energy range of 4d → nf transitions, which occur within or adjacent to the 13.5 nm window for extreme ultraviolet lithography light source development. The reported values allow the quantification of opacity effects in xenon plasmas due to these 4d → nf autoionizing states. The oscillator strengths for the 4d → 4f and 4d → 5f transitions in Xe q+ ͑q =1-6͒ ions are calculated using nonrelativistic Hartree-Fock and random phase approximations. These are compared with published experimental values for Xe + to Xe 3+ and with the values obtained from the present experimental cross-section measurements for Xe 4+ to Xe 6+ . The calculations assisted in the determination of the metastable content in the ion beams for Xe 5+ and Xe 6+ . The experiments were performed by merging a synchrotron photon beam generated by an undulator beamline of the Advanced Light Source with an ion beam produced by an electron cyclotron resonance ion source.
Laser-Driven Ionization and Photoabsorption Spectroscopy of Atomic Ions
Lasers, Spectroscopy and New Ideas, 1987
The application of laser-driven ionization techniques to photoabsorption spectroscopy of atomic ions will be discussed. A summary of the experimental results which confirm that a collisional mechanism is responsible for the nearly complete ioniza tion following laser irradiation is gi yen along with a bibliography of the photoabsorption measurements reported to date. The importance of these investigations, demonstrated in two studies involving the Ba nuclear sequence (Le., Ba, Ba+, and Ba H) and the Xe isoelectronic sequence(i.e., Xe, Cs+ and Ba++), will be discussed. Finally, a tabulation of quantum defect parameters for Xe, Cs + and Ba H based on are-analysis of the Xe-sequence spectra via a shifted R-matrix quantum defect approach,will be presented.
High-Resolution Measurements of Photoionization of Ions Using Synchrotron Radiation
AIP Conference Proceedings
Measurement of absolute cross sections for photoionization of ions has become feasible by merging a wellcollimated ion beam with a monochromatic beam of synchrotron radiation. An electron cyclotron resonance (ECR) ion source permits such measurements to be extended to multiply charged ions, and makes possible systematic studies along isoelectronic sequences. The evolution of atomic spectra along such sequences is commonly studied theoretically, but the predictive ability of the theoretical methods remains largely untested. Absolute cross-section measurements are presented for the first three ionic members of the isoelectronic sequence of nitrogen (O + , F 2+ and Ne 3+).
The Absolute Cross Section forL‐Shell Photoionization of C+Ions from Threshold to 105 eV
The Astrophysical Journal Supplement Series, 2001
The absolute cross section for photoionization of C`ions has been measured from the ionization threshold at 24 eV to 105 eV by overlapping an ion beam with a monochromatized synchrotronradiation beam from the ASTRID undulator. The measurements, which are important for astrophysical modeling of, for example, stellar atmospheres, have been compared with R-matrix calculations from the Opacity Project and the Iron Project. The general agreement between theory and experiment is good, yet di †erences in the magnitude of the cross section of up to 50% are observed as well as some deviations concerning the resonance structure. Subject headings : atomic data È atomic processes
Photoionization of Multiply Charged Ions at the Advanced Light Source
AIP Conference Proceedings, 2005
Photoionization of multiply charged ions is studied using the merged-beams technique at the Advanced Light Source. An ion beam is created using a compact 10-GHz all-permanent-magnet ECR ion source and is accelerated with a small accelerator. The ion beam is merged with a photon beam from an undulator to allow interaction over an extended path. Absolute photoionization cross sections have been measured for a variety of ions along both isoelectronic and isonuclear sequences. FIGURE 1. Schematic diagram of ion-photon mergedbeams end station.
Photoionization study of Xe 5s: ionization cross sections and photoelectron angular distributions
Journal of Physics B: Atomic, Molecular and Optical Physics, 2014
We report studies of photoelectron angular distribution and cross-section for photoionization of xenon 5s electrons using the relativistic multiconfiguration Tamm-Dancoff (MCTD) approximation. We find that MCTD provides a significantly improved agreement with experiment, compared to some of the other relativistic many body approximations such as the relativistic random phase approximation and the relativistic random phase approximation with relaxation, over the entire photon energy region bracketing the near-threshold 5s Cooper minimum, from the 5s threshold up to about 70 eV. The MCTD results in the length form are in much better agreement with the experiment than those in the velocity form, suggesting residual correlations that must be of importance.