Photoionization cross sections of halogen-like Kr+ and Xe+ ions have been measured in the photon energy range extending up to 15 eV above the threshold. Two different devices were used, a merged-beam set-up and an ion trap. Combination of the two techniques allows for the extraction of the pure ground state ionization cross section on an absolute scale. Multiconfiguration Dirac–Fock calculations reproduce the magnitude of the direct photoionization cross sections well.

We have measured the absolute photoionization cross sections of ${\text{Fe}}^{2+}$ to ${\text{Fe}}^{6+}$ ions in the photon energy range covering the first ionization threshold up to 160 eV. Particular interest is emphasized on the region of the $3p\ensuremath{\rightarrow}3d$ excitations. The experimental data are compared to the results of calculations we have performed using a spectral opacity code, as well as to available $R$-matrix and one-electron calculations. It is shown that often the theoretical results tend to overestimate the intensity of the $3p\ensuremath{\rightarrow}3d$ photoexcitations. An anomalously low value of the integrated oscillator strength is measured for ${\text{Fe}}^{2+}$ ion.

We present measurements of the absolute photoionization cross section of the neonlike Si4+ ion over the 110-184 eV photon energy range. The measurements were performed using two independent merged-beam setups at the super-ACO and ASTRID synchrotron-radiation facilities, respectively. Signals produced in the photoionization of the 2p subshell of the Si4+ ion both from the 2p(6) S-1(0) ground state and the 2p(5)3s P-3(0,2) metastable levels were observed. Calculations of the 2p photoionization cross sections were carried out using a multi-configuration Dirac-Fock code. They give results in good agreement with the measured spectra. Comparison with other available theoretical results is also presented.

The merged-beams technique, which consists in merging an ion beam with a synchrotron radiation beam, allows to determine absolute photoionization cross sections on ionic species. In this poster, we will discuss recent results we have obtained on ions of the iron isonuclear sequence in the photon energy range covering the first ionization threshold up to 160 eV. Future developments of the experiments at SOLEIL will be also presented.

Absolute measurements of the photoionization cross sections of the singly charged ions in the sequence Ca to Ni are presented, focussing on the 3p ->. 3d resonance region. Major differences are found in both spectral structure and cross section as the 3d shell is filled progressively. The behaviour of the total oscillator strength is studied as well as its relation to the collapse of the 3d orbital. The 3p(5)3d P-1 term is found to have an influence on the spectra even when further 3d electrons are added and this dependence combined with the effect of Hund's rule leads to a considerable simplification in the structure of the absorption spectra before the half-filled 3d shell, while from the half-filled 3d shell Hund's rule is the main simplifying effect.

Photoionization spectra have been recorded in the $4s$, $4p$, and $3d$ resonance regions for the Kr I isoelectronic sequence using both the dual laser produced plasma (DLP) technique (at DCU) to produce photoabsorption spectra, and the merged ion beam and synchrotron radiation technique (at ASTRID) to measure absolute photoionization cross sections. Profile parameters are compared for the $4s\text{\ensuremath{-}}np$ resonances of ${\mathrm{Rb}}^{+}$ and ${\mathrm{Sr}}^{2+}$. Many $4p\ensuremath{\rightarrow}ns$, $md$ transitions are identified with the aid of Hartree-Fock calculations, and consistent quantum defects are observed for the various $ns$ and $md$ Rydberg series. Absolute single and double photoionization cross sections recorded in the $3d$ region for ${\mathrm{Rb}}^{+}$ and ${\mathrm{Sr}}^{2+}$ ions show preferential decay via double photoionization. This is only the second report to our knowledge where both the DLP technique and the merged-beam technique have been used simultaneously to record photoionization spectra, and the advantages of both techniques (i.e., better resolution in the case of DLP and values for absolute photoionization cross sections in the case of the merged-beam technique) are highlighted.

We have measured the absolute photoionization cross section of the Fe4+ ion between 59 and 140 eV photon energy, including the region of the 3p -> 3d excitations. To interpret the data we have performed calculations using a code developed for the determination of the spectral opacity of hot plasmas. We have also compared our measurements with the results of several R-matrix calculations. In short, both theoretical approaches describe qualitatively the results of the experiment in the 3p-3d excitation region.

Be-like Ag43+, Sn46+, and Xe50+ ions were produced by beam-foil excitation at the UNILAC accelerator of the GSI. The wavelengths of the 2s2 1S0–2s2p 3P1 intercombination lines were measured using the GSI 5 m grazing incidence spectrometer. The projectile spectra were calibrated in situ with well known ionic lines of a VUV Penning discharge lamp. A precise determination of the Doppler shift was necessary. An experimental precision of 10-4 was realized. Our medium-Z experimental results represent the heaviest Be-like ions studied. They are compared with published MCDF and MBPT calculations along the isoelectronic Be-like series. Excellent agreement exists between our Xe-value and a recent result from an electron beam ion trap.

Be-like Ag43+, Sn46+, and Xe50+ ions were produced by beam-foil excitation at the UNILAC accelerator of the GSI. The wavelengths of the 2s(2) S-1(0)-2s2p 3p(1) intercombination lines were measured using the GSI 5 m grazing incidence spectrometer. The projectile spectra were calibrated in situ with well known ionic lines of a VUV Penning discharge lamp. A precise determination of the Doppler shift was necessary. An experimental precision of 10(-4) was realized. Our medium-Z experimental results represent the heaviest Be-like ions studied. They are compared with published MCDF and MBPT calculations along the isoelectronic Be-like series. Excellent agreement exists between our Xe-value and a recent result from an electron beam ion trap.

Absolute photoionization cross sections for the ions N2+, N3+, O3+, O4+, F3+, F4+ and Ne4+ are measured using the merged-beam technique, combining the synchrotron radiation from an undulator at the storage ring ASTRID with ions produced by an ECR ion source. The spectral structures and the development of the cross sections along iso-electronic sequences are discussed. The experimental data are compared with R-matrix calculations from the Opacity Project and other sources, MCDF calculations, as well as the model functions provided by verner et al. (1996). In general, good agreement between experiment and calculations is observed for the magnitude of the continuum cross sections whereas very significant discrepancies are present for the resonance structures. The experimental data are also available in electronic form at the CDS.

High-resolution photoionization cross section measurements have been made at the ALS, corresponding to the 2p excitation (photon energy > 80 eV) of the AlII ground state 2p63s2. Previous absolute measurements from ASTRID are available for energies 20–160 eV. R-matrix calculations have been carried out and comparison is made with the measured data. In the near threshold region (<25 eV), theory predicts two 3pns 3Po resonance series, a 3pns 1Po and a 3pnd 1Po series. The experiment detects a single 3pns series and we find excellent agreement with the theoretical positions. Above the 2p ionization threshold, the ALS data show much more detail and by comparing with oscillator strengths and resonance positions with the calculation we identify much of the resonant structure.

Be-like Ag43+, Sn46+, and Xe50+ ions were produced by beam-foil excitation at the UNILAC accelerator of the GSI. The wavelengths of the 2s2 1S0–2s2p 3P1 intercombination lines were measured using the GSI 5 m grazing incidence spectrometer. The projectile spectra were calibrated in situ with well known ionic lines of a VUV Penning discharge lamp. A precise determination of the Doppler shift was necessary. An experimental precision of 10-4 was realized. Our medium-Z experimental results represent the heaviest Be-like ions studied. They are compared with published MCDF and MBPT calculations along the isoelectronic Be-like series. Excellent agreement exists between our Xe-value and a recent result from an electron beam ion trap.

The absolute cross section for photoionization of Mn(+) has been measured using the merged-beam technique, focusing on the region of the 'giant' 3p --> 3d resonance. The main discrepancy between theory and earlier experiments has been removed. However, more extensive relativistic calculations are required for a rigorous comparison with theory.

Bound $4d$ inner-shell excited states have been observed as $4{d}^{10}5{s}^{2}5{p}^{5}\ensuremath{\rightarrow}4{d}^{9}5{s}^{2}5{p}^{6}\phantom{\rule{0.3em}{0ex}}^{2}D_{5∕2,3∕2}$ Feshbach resonances in the photodetachment spectrum of ${\text{Te}}^{\ensuremath{-}}$ utilizing the merged-beam technique at the storage ring ASTRID. The strong binding of these core-excited levels, 2.95 and $1.47\phantom{\rule{0.3em}{0ex}}\text{eV}$ respectively, is attributed to the extra stability of the full $5p$ shell. The role of the present data as a prototype spectrum for negative ions having an outer shell with a single vacancy in the initial state is discussed.

Measurement of absolute cross sections for photoionization of ions has become feasible by merging a well‐collimated 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+, F2+ and Ne3+).

The absolute cross section for photoionization of Cr(+) has been measured using the merged-beam technique, focusing on the region of the 'giant' 3p --> 3d resonance. These new absolute data differ considerably from previous experimental data, with the result that the agreement between experiment and existing calculations has improved substantially. The neutral and ionized Cr spectra, previously believed to be completely different, are shown here to be rather similar. The role of the 3d(5)((6)S) state in determining the special position of Cr among the 3d elements is emphasized. The experimental data are available at http://www.phys.au.dk/amo/atomphys/atomphys.htm.

High-resolution measurements of the photoionization cross sections of the Na-isoelectronic ions Mg+ and Al2+ are presented, to be compared with earlier measurements in which structure in the most prominent peaks was unresolved. These measurements have been normalized to the earlier ones in order to provide values of the oscillator strengths of the newly resolved peaks, and comparison is made with multiconfiguration Hartree-Fock calculations.

The photon-ion merged beam technique has been used to measure the ionization cross sections of I-, Cs+, Ba+ and Ba2+ ions in the energy region from 40 to 185 eV, which is dominated by photoexcitation from the 4d shell (the experimental data are available at http://www.ifa.au.dk/amo/atomphys/atomphys.htm). Within the experimental accuracy, the total oscillator strengths for these ions and for the I+, I2+, Xe+ and Xe2+ ions, that were recently studied by some of the present authors, are identical, with the contribution from the 4d → np or nf resonances becoming more important with increasing nuclear charge and ionization stage, and with the maximum value of the continuum cross section increasing as the nuclear number is enlarged. The present data support the assumption that the 4f wavefunctions contract gradually with increasing ionization, both along isonuclear and isoelectronic sequences, for ionic charges ranging from -1 to +2.