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A merged-beam technique is used to measure charge transfer (CT) cross sections for the (O2+, D) and (CO+, D) systems over a wide range of collision energy from 20 eV/u to 2 keV/u. At the higher energies where the collision is rovibrationally frozen and the differences in the Q values ofthe CT process can be neglected, the cross sections all converge to (7.5 ±0.5) x 10-16 cm2 at 2 keV/u and are consistent with a rovibrational frozen (H2+ ,H) calculation. Toward lower velocities, (O2+, D) and (CO+, D) have consistently similar cross sections but diverge below 60 eV/u. In contrast, previously reported merged-beam measurements for (D2+, H), a system with fewer electrons on the molecular core, no electronic excited states, and relatively fewer charge transfer channels, shows a decreasing cross section toward lower energies. These different trends are compared to previous merged-beam measurements of charge transfer with H for several atomic 4+ ions (Si4+, Ne4+, N4+, and C4+) which have a variety of electrons on the core. [ABSTRACT FROM AUTHOR]

Lyman spectra and line ratios are reported for soft-x-ray emissions following the charge exchange process in 293, 414, 586, and 1256 km/s O8+ and Kr collisions. Lyman series from Ly- α to Ly- ɛ were resolved for the O7+ ion using a high-resolution x-ray quantum microcalorimeter detector. It is found that the observed line ratios are dependent on the n l distribution of the captured electron, and the Ly- α and Ly- β x-ray emissions are enhanced. Moreover, by comparing the measured line ratios to the constructed theoretical single charge exchange line ratios for O8+ + H, it is suggested that autoionizing double capture plays a significant role in the enhancement of Ly- α and Ly- β emissions for the present system. [ABSTRACT FROM AUTHOR]

X-ray spectra following charge-exchange collisions between C6+ and He are presented for collision energies between 460 and 32 000 eV/u. Spectra were obtained at the Oak Ridge National Laboratory Multicharged Ion Research Facility using a microcalorimeter x-ray detector capable of fully resolving the C VI Lyman series lines through Ly-γ. These line ratios are sensitive to the initial electron I distribution and test our understanding of the charge-exchange process. In addition, these line ratios are important for identifying charge exchange in astrophysical contexts involving the interaction of solar wind ions with neutrals. Our measurements are performed at collision velocities (300-2500 km/s) which overlap most of the solar wind range. Additional data of this type can be combined with computations to provide an extensive set of reliable line ratios and absolute cross sections for the interpretation of a variety of astrophysical situations [ABSTRACT FROM AUTHOR]

The collision-energy resolved rate coefficient for dissociative recombination of HD+ ions in the vibrational ground state is measured using the photocathode electron target at the heavy-ion storage ring TSR. Rydberg resonances associated with rovibrational excitation of the HD+ core are scanned as a function of the electron collision energy with an instrumental broadening below 1 meV in the low-energy limit. The measurement is compared to calculations using multichannel quantum defect theory, accounting for rotational structure and interactions and considering the six lowest rotational energy levels as initial ionic states. Using thermal-equilibrium-level populations at 300 K to approximate the experimental conditions, close correspondence between calculated and measured structures is found up to the first vibrational excitation threshold of the cations near 0.24 eV. Detailed assignments, including naturally broadened and overlapping Rydberg resonances, are performed for all structures up to 0.024 eV. Resonances from purely rotational excitation of the ion core are found to have similar strengths as those involving vibrational excitation. A dominant low-energy resonance is assigned to contributions from excited rotational states only. The results indicate strong modifications in the energy dependence of the dissociative recombination rate coefficient through the rotational excitation of the parent ions, and underline the need for studies with rotationally cold species to obtain results reflecting low-temperature ionized media. [ABSTRACT FROM AUTHOR]