SIMBAD references

Electron-ion recombination rate coefficients for beryllium-like calcium ions in the center of mass energy from 0 to 51.88 eV have been measured by means of the electron-ion merged-beam technique at the main cooler storage ring at the Institute of Modern Physics in Lanzhou, China. The measurement energy range covers the dielectronic recombination (DR) resonances associated with the 2s²¹S₀→2s2p³P_0,1,2,¹P₁ core excitations and the trielectronic recombination (TR) resonances associated with the 2s²¹S₀→2p²³P_0,1,2,¹D₂,¹S₀ core excitations. In addition, the AUTOSTRUCTURE code was used to calculate the recombination rate coefficients for comparison with the experimental results. Resonant recombination originating from parent ions in the long-lived metastable state 2s2p³P₀ ions has been identified in the recombination spectrum below 1.25 eV. A good agreement is achieved between the experimental recombination spectrum and the result of the AUTOSTRUCTURE calculations when fractions of 95% ground-state ions and 5% metastable ions are assumed in the calculation. It is found that the calculated TR resonance positions agree with the experimental peaks, while the resonance strengths are underestimated by the theoretical calculation. Temperature dependent plasma rate coefficients for DR and TR in the temperature range of 10³-10⁸ K were derived from the measured electron-ion recombination rate coefficients and compared with the available theoretical results from the literature. In the temperature range of photoionized plasmas, the presently calculated rate coefficients and the recent results of Gu & Colgan et al. are up to 30% lower than the experimentally derived ones, and the older atomic data are even up to 50% lower than the present experimental result. This is because strong resonances situated below electron-ion collision energies of 50 meV were underestimated by the theoretical calculation, which also has a severe influence on the rate coefficients in low-temperature plasmas. In the temperature range of collisionally ionized plasmas, agreement within 25% was found between the experimental result and the present calculation as well as the calculation by Colgan et al. The present result constitutes a set of benchmark data for use in astrophysical modeling.