Aims. The interpretation of astrophysical spectra depends directly on a knowledge of the ionization state of the emitting plasma. This is determined, in part, from collisional ionization rate coefficients. The most recent assessments of these were performed by Arnaud & Rothenflug (1985, A&AS, 60, 425) and Arnaud & Raymond (1992, ApJ, 398, 394). Since their work, new laboratory measurements of ionization cross sections have become available as well as the Flexible Atomic Code (FAC) which enables theoretical calculations of these rates. Our goal is to provide a complete set of ionization rate coefficients for the elements hydrogen through zinc. Methods. A scaling law, which assists the analysis of ionization cross sections and rate coefficients, has been developed following the approach of Burgess & Tully (1992, A&A, 254, 436). Essentially all available measured cross sections along each isoelectronic sequence have been examined and compared to cross sections calculated with the Flexible Atomic Code (FAC) and with other calculations. Two approaches has been taken to provide a complete set of ionization cross sections. In the first, fits to scaled measured ionization cross sections, particularly for neutral and singly ionized species, are performed. In the second, fits to scaled calculated direct ionization and excitation-autoionization cross sections are performed to provide the remainder of the set. The fits to the cross sections are then integrated over a Maxwellian velocity distribution to derive ionization rate coefficients. Results. A complete set of ground level ionization cross sections and rate coefficients has been developed through the combination of these two approaches. A tabulation of parameter fits to ground level ionization rate coefficients for all atoms and ions of the elements of H through Zn is provided.

/pdf/ionization-rate-coefficients-for-the-elements-hydrogen-376eb006r3.pdf

Ionization rate coefficients for the elements hydrogen through zinc

The available atomic data used for interpreting and modeling x-ray observations are reviewed The applications for these data can be divided into several levels of detail, ranging from compilations which can be used with direct inspection of raw data, such as line finding lists, to synthetic spectra which attempt to fit to an entire observed dataset simultaneously This review covers cosmic sources driven by both electron ionization and photoionization and touches briefly on planetary surfaces and atmospheres The applications to x-ray astronomy, the available data, and recommendations for astronomical users are all reviewed, and an attempt to point out the applications where the shortcomings are greatest is also given

http://ned.ipac.caltech.edu/level5/Sept06/Kallman/paper.pdf

Atomic data for x-ray astrophysics

We investigate the heating of the quasifree electrons in large rare-gas clusters ($N$ exceeding ${10}^{5}$ atoms) by short laser pulses at moderate intensities ($I\ensuremath{\simeq}{10}^{15}\text{ }\text{ }\mathrm{W}\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$). We identify elastic large-angle backscattering of electrons at ionic cores in the presence of a laser field as an efficient heating mechanism. Its efficiency as well as the effect of collective electron motion, electron-impact ionization, and cluster charging are studied employing a mean-field classical transport simulation. Results for the absolute x-ray yields are in surprisingly good quantitative agreement with recent experimental results.

Laser-cluster interaction: x-ray production by short laser pulses.

http://absimage.aps.org/image/DAMOP06/MWS_DAMOP06-2006-000073.pdf

Laser-Cluster Interaction: X-Ray Production by Short Laser Pulses

Absolute cross section measurements for electron-impact single ionization of Ne-q+ (q = 4-8) ions and for double ionization of Ne5+ and Ne6+ are reported. The animated crossed-beams method has been applied. The measurements cover the energy range from threshold to several keV. The Ne4+ and Ne6+ ion beams are found to contain an important population of ions formed in metastable states. For single ionization, results are in overall good agreement with direct ionization theoretical predictions, when available. Excitation-autoionization is observed in the ionization threshold region for Ne4+ and in the K-L transition energy region for Ne6+ and Ne7+. Double ionization of Ne5+ and Ne6+ is found to be dominated by K-shell ionization followed by autoionization.

https://iopscience.iop.org/article/10.1088/0953-4075/30/3/025/pdf

Electron-impact ionization of neon ions (q=4-8)

The first absolute cross section measurements for single and double electron impact ionization of sodium-like Ar7+ are reported. The animated crossed beams method has been employed in the energy range from threshold to 3000 eV. The measured cross sections for single ionization are higher than the theoretical and semi-empirical predictions by about 20-50%. This discrepancy has been associated with the contribution of the indirect ionization processes. The double ionization cross section is only 1% of the single one.

Absolute Cross-section Measurements for Electron-impact Ionization of Ar-7+

Absolute cross sections for electron impact ionization of multiply charged argon ions (Arq+) have been measured in an animated crossed electron-ion beam experiment. Results are reported for single ionization (SI) (q = 4-6, 8, 10 and 11) ions and for double ionization (DI) (q = 5-11). The measurements cover the energy range from threshold to about 6000 eV The direct process is seen to dominate SI for q = 8, 10 and 11. For charge states 4-6, excitation-autoionization processes are seen to largely contribute to the ionization signal. In addition, metastable states are unambiguously identified for Ar5+ and Ar6+. Ionization-autoionization (IA) from the L shell accounts predominantly for DI of Arq+ (q = 5, 6). For charge states 7-11 direct DI is found to decrease strongly with respect to IA from the K shell.

http://iopscience.iop.org/article/10.1088/0953-4075/35/18/304/pdf

Electron impact ionization of argon ions (q=4-11)

Absolute cross-sections for single ionisation of helium-like C4+ and O6+ by electron impact have been measured for incident electron energy ranging from below the expected metastable state ionisation threshold to 3 keV. A crossed electron-ion beam setup has been used in this experiment. From analysis of the ion time of flight, it is concluded that the signal observed below the ground state ionisation threshold can only be due to the triplet state 2 3S. The importance of the various ionisation processes is discussed for this particular state. We present also a calculation of the branching ratio for autoionisation following the electron impact excitation from one of the two metastable states to the doubly excited states of the 2l,2l' configurations. The metastable population has been estimated to 16.3% for C4+ and 3.9% for O6+.

M. Duponchelle

Papers

Absolute Cross-section Measurements for Electron-impact Ionization of Ar-7+

Electron impact ionization of argon ions (q=4-11)

Electron-impact Ionization of C4+ and O6+