Electron–ion recombination of Be-like ⁴⁰Ar¹⁴⁺ has been measured by employing the electron–ion merged-beams method at the cooler storage ring CSRm. The measured absolute recombination rate coefficients for collision energies from 0 to 60 eV are presented, covering all dielectronic recombination (DR) resonances associated with 2s ² → 2s2p core transitions. In addition, strong trielectronic recombination (TR) resonances associated with 2s ² → 2p ² core transitions were observed. Both DR and TR processes lead to series of peaks in the measured recombination spectrum, which have been identified by the Rydberg formula. Theoretical calculations of recombination rate coefficients were performed using the state-of-the-art multi-configuration Breit–Pauli atomic structure code AUTOSTRUCTURE to compare with the experimental results. The plasma rate coefficients for DR+TR of Ar¹⁴⁺ were deduced from the measured electron–ion recombination rate coefficients in the temperature range from 10³ to 10⁷ K, and compared with calculated data from the literature. The experimentally derived plasma rate coefficients are 60% larger and 30% lower than the previously recommended atomic data for the temperature ranges of photoionized plasmas and collisionally ionized plasmas, respectively. However, good agreement was found between experimental results and the calculations by Gu and Colgan et al. The plasma rate coefficients deduced from experiment and calculated by the current AUTOSTRUCTURE code show agreement that is better than 30% from 10⁴ to 10⁷ K. The present results constitute a set of benchmark data for use in astrophysical modeling.

We measured the kinetic energy distributions of the fragment ions of doubly and quadruply ionized argon dimers using 3000 eV electron impact. For the dissociation of (Ar${}_2$)${}^{2+}$, the peak that indicates radiative charge transfer is observed, where the outer-shell ionization (dominant in highly charged ion collision) and the inner-shell ionization (preferential in x-ray experiments) have approximately equal contributions. For the dissociation of (Ar${}_2$)${}^{4+}$, the interatomic Coulombic decay and electron-transfer-mediated decay are first observed in the electron-impact process.

Charge exchange between highly charged ions and neutral atoms and molecules has been considered as one of the important mechanisms controlling soft X-ray emissions in many astrophysical objects and environments. However, for modeling charge exchange soft X-ray emission, the data of n- and l-resolved state-selective capture cross sections are often obtained by empirical and semiclassical theory calculations. With a newly built cold target recoil-ion momentum spectroscopy (COLTRIMS) apparatus, we perform a series of measurements of the charge exchange of Ne^(8,9)+ ions with He and H₂ for collision energy ranging from 1 to 24.75 keV/u. n-resolved state-selective capture cross sections are reported. By comparing the measured state-selective capture cross sections to those calculated by the multichannel Landau–Zener method (MCLZ), it is found that MCLZ calculations are in good agreement with the measurement for the dominant n capture for He target. Furthermore, by using nl-resolved cross sections calculated by MCLZ and applying l distributions commonly used in the astrophysical literature to experimentally derived n-resolved cross sections, we calculate the soft X-ray emissions in the charge exchange between 4 keV/u Ne⁸⁺ and He by considering the radiative cascade from the excited Ne⁷⁺ ions. Reasonable agreement is found in comparison to the measurement for even and separable models, and MCLZ calculations give results in a better agreement.

An experimental investigation of the breakup of ${\left(\mathrm{C}{\mathrm{O}}_2\right)}^{3+}$ induced by $\mathrm{N}{\mathrm{e}}^{4+}$ ion impact at incident energies of 1.12 MeV was performed. By analyzing the momentum distributions and the kinetic energies of the three fragment ions, the nonsequential and sequential dissociation mechanisms are verified. In contrast to highly charged ion impact, two different sequential decay pathways were observed in the present experiment. One pathway originates from the primary cation ${\left(\mathrm{C}{\mathrm{O}}_2\right)}^{3+}$ populated into ${}^4\mathrm{\Sigma }^{+}$ states by collision charge exchange and its daughter cation ${\left(\mathrm{CO}\right)}^{2+}$ populated into the two excited states (${}^3\mathrm{\Pi }$ and $X{}^1\mathrm{\Pi }$) by the first fragmentation step, resulting in a lower KER peak. The other pathway originates from the primary cation ${\left(\mathrm{C}{\mathrm{O}}_2\right)}^{3+}$ locating at ${}^6\mathrm{\Pi }$ state, and its daughter cation ${\left(\mathrm{CO}\right)}^{2+}$ populated into the metastable excited states ${}^3\mathrm{\Pi }$, $X{}^1\mathrm{\Pi }$, and ${}^3\mathrm{\Sigma }^{+}$, leading to the higher KER peak. Our work is a breakup experiment of ${\left(\mathrm{C}{\mathrm{O}}_2\right)}^{3+}$ presenting the initial states of the parent cation ${\left(\mathrm{C}{\mathrm{O}}_2\right)}^{3+}$ and the metastable states of $\mathrm{C}{\mathrm{O}}^{2+}$ ion simultaneously.