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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2641setu.eps} \end{figure}$ Figure 1: The experimental set-up. UN/MO: photon beam from the undulator/Miyake-monochromator beam line at the ASTRID storage ring; I: ECR ion source; EL: Einzel lens; M1 and M2: deflection magnets; ED: Electrostatic deflector; IC: interaction chamber (biased); FC1, FC2 and FC3: Faraday cups; PD: calibrated photodiode; D1 and D2: particle detectors. FC1, FC3 (for negative ions) and D2 were not used in the present experiments.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2641He.eps} \end{figure}$ Figure 2: The photoionization cross section of ³He⁺ ions - a test of the experimental accuracy. Theory: line; absolute cross section measurement: circles and statistical error bars.
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In the text

$\begin{figure} \par\includegraphics[width=17.5cm,clip]{2641b-li.EPS} \end{figure}$ Figure 3: The absolute photoionization cross sections (in Mb = $10^{-18} ~{\rm cm} ^2$ ) as a function of the photon energy (eV) for the B-like ions N²⁺ ( left), O³⁺ ( center) and F⁴⁺ ( right). Top: present experimental data; middle: R-matrix calculations; bottom: MCDF calculations. The R-matrix data by Fernley et al. (1999, obtained from the Opacity Projects TOPbase) are shown by the (black) solid line, whereas newer data for N²⁺ (Nahar & Pradhan 1997) are shown by the (green) dotted line. The theoretical spectra have been convoluted with Gaussians of 100, 250 and 500 meV ( FWHM), respectively, and are calculated under the assumption of a (⁴P:²P) fraction of (0.90:0.10) for N²⁺ and F⁴⁺ and (0.84:0.16) for O³⁺. The MCDF data are from the present work (N²⁺ and F⁴⁺) or by Champeaux et al. (2003, O³⁺). The numbers refer to Tables 2-4. The experimental data for N²⁺ and O³⁺ are shown enlarged in Figs. 4 and 5, respectively.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2641Niii.eps} \end{figure}$ Figure 4: The measured photoionization cross sections of N²⁺ with the different Rydberg series indicated. The numbers refer to Table 2. The Rydberg series are extrapolated utilizing the series limits and lower-lying members with known energy (NIST 1999).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2641Oiv.eps} \end{figure}$ Figure 5: The measured photoionization cross sections of O³⁺ with the different Rydberg series indicated ( top graph). The numbers refer to Table 3. The Rydberg series are extrapolated utilizing the series limits and lower-lying members with known energy (NIST 1999). Also shown are the R-matrix calculations from Nahar (1998, <)458#> middle# and Nahar (2004, <)460#> bottom#. The theoretical spectra have been convoluted with Gaussians of 250 meV ( FWHM) and are calculated under the assumption of a 16% fraction of ions in the metastable states.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{2641be-l.EPS} \end{figure}$ Figure 6: The absolute photoionization cross sections (in Mb = $10^{-18} ~{\rm cm} ^2$ ) as a function of the photon energy (eV) for the Be-like ions N³⁺ ( left), O⁴⁺ ( right). Top: present experimental data; middle: R-matrix calculations; bottom: MCDF calculations. The R-matrix data are by solid (black) line, Tully et al. (1990, obtained from the Opacity Projects TOPbase) with newer data by Nahar (2004, dotted (green) line) and the MCDF data are part of the present work (N³⁺) or by Champeaux et al. (2003, O⁴⁺). The theoretical spectra have been convoluted with Gaussian distributions of 230 and 250 meV ( FWHM), respectively, and are calculated under the assumption of a (³P:¹P) fraction of (0.35:0.65) for N³⁺ and (0.50:0.50) for O⁴⁺. The numbers refer to Tables 7 and 8.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2641Fiv.eps} \end{figure}$ Figure 7: The absolute photoionization cross sections of F³⁺. The numbers refer to Table 10. The Rydberg series are extrapolated utilizing the series limits and lower-lying members with known energy (NIST 1999).
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In the text

$\begin{figure} \includegraphics[width=12cm,clip]{2641c-li.EPS} \end{figure}$ Figure 8: The absolute photoionization cross sections (in Mb = $10^{-18} ~\rm {\rm cm}^2$ ) as a function of the photon energy (eV) for the C-like ions F³⁺ ( left) and Ne⁴⁺ ( right). Top: present experimental data; middle: R-matrix calculations; bottom: MCDF calculations. The R-matrix data by Lou & Pradhan (1989, obtained from the Opacity Projects TOPbase) are shown by (black) solid line, whereas the data by (Nahar & Pradhan 1997, ground state only) are shown by (green) dotted line for F³⁺. The theoretical spectra have been convoluted with Gaussians of 300 and 550 meV ( FWHM), respectively, and are calculated under the assumption of a (³P:¹D:¹S:⁵S) fraction of (68:30:0:2) for F³⁺ and (56:36:6:2) for Ne⁴⁺. The MCDF data are part of the present work, and the numbers refer to Tables 10 and 11. The experimental data for F³⁺ are shown enlarged in Fig. 7.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2641He.eps} \end{figure}$	Figure 2: The photoionization cross section of ³He⁺ ions - a test of the experimental accuracy. Theory: line; absolute cross section measurement: circles and statistical error bars.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2641Niii.eps} \end{figure}$	Figure 4: The measured photoionization cross sections of N²⁺ with the different Rydberg series indicated. The numbers refer to Table 2. The Rydberg series are extrapolated utilizing the series limits and lower-lying members with known energy (NIST 1999).
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2641Fiv.eps} \end{figure}$	Figure 7: The absolute photoionization cross sections of F³⁺. The numbers refer to Table 10. The Rydberg series are extrapolated utilizing the series limits and lower-lying members with known energy (NIST 1999).
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