Electron emission from the single-electron capture with simultaneous single ionization in 30 keV/u He2+ on argon was investigated using a reaction microscope, providing the electron energy spectra and momentum distributions. Intensive peaks for electrons with near-zero kinetic energies have been observed. It is demonstrated that mechanisms contributing to the electron emission include direct transfer ionization (DTI), double-electron capture with autoionization (DECA), and single-electron capture with autoionization (SECA) of target. Comparison of resonance energies shows that Ar+ ions in SECA decay mainly through the 3s3p53d states by emitting Auger electrons, and He** in DECA decay through the 2l2l$'${} states. The dependence of electron emission on the transverse momentum exchange has been studied. In the transfer ionization channel studied here, the DTI process dominates the electron emission, and no saddle point electron mechanism has been found.

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.

A combined experimental and theoretical study on single capture in 30- and 100-keV ${\mathrm{He}}^{+}$ on He collisions was performed. By using a reaction microscope, we obtained the state selective cross sections and the angular-differential cross sections. It was found that the experimental state-selective cross sections were in good agreement with the dynamic screening classical trajectory Monte Carlo calculation for 100-keV ${\mathrm{He}}^{+}$ incident. The comparisons with various versions of such calculations reveal the roles played by different electron-electron correlation effects. Moreover, a prominent oscillatory structure was observed in the angular-differential cross sections for both projectile energies. With the single capture probability distribution obtained from the classical trajectory Monte Carlo calculation, the oscillation structures can be well explained by atomic-size Fraunhofer-type diffraction.

A combined experimental and theoretical study on single capture in 15–$50\mathrm{keV}/\mathrm{u}{\mathrm{C}}^{4+} +$ He collisions was performed. State-selective single-electron capture cross sections and projectile scattering angle distributions were obtained by using a reaction microscope. A comparison of the state-selective cross sections with theoretical calculations based on the two-active-electron semiclassical atomic-orbital close-coupling method showed an excellent agreement for the considered impact energies. For the angular differential cross sections, an overall agreement was also obtained between the present experimental and theoretical results. Simulations performed using an extended Fraunhofer-type diffraction model suggest that the undulatory structures observed at small scattering angles for capture to ${\mathrm{C}}^{3+}(1s^{2}2s$) and ${\mathrm{C}}^{3+}(1s^{2}2p_0$) can be interpreted as the diffraction pattern of the incident projectile de Broglie wave confined by an aperture defined as the region around the target where the considered capture process is likely. The strong competition between single-electron capture to ${\mathrm{C}}^{3+}(1s^{2}2p_0$) and ${\mathrm{C}}^{3+}(1s^{2}2p_1$) is also discussed to interpret the differences observed between their respective differential cross sections.