[en] The transmission of 10-18 keV O^- ions through Al₂O₃ nano-capillaries has been investigated experimentally. From the angular distribution of the transmitted particles, O⁰ and O^- and O⁺ ions can be distinguished in the mixed scattered beams. The fractions of the scattered ions increase with both the tilt angle and the incident energy, which indicates strongly that there is dynamical charge exchange in the scattering of negative ions on the insulator surface. Moreover, it is found that the scattered neutrals (O⁰) are only more or less guided along the capillary axis, which is greatly different from the case of the guiding effect of highly charged ions.

[en] Advances in merged-beams instruments have allowed experimental studies of the mutual neutralization (MN) processes in collisions of both Li⁺ and Na⁺ ions with D⁻ at energies below 1 eV. These experimental results place constraints on theoretical predictions of MN processes of Li⁺ and Na⁺ with H⁻, important for non-LTE modeling of Li and Na spectra in late-type stars. We compare experimental results with calculations for methods typically used to calculate MN processes, namely the full quantum (FQ) approach, and asymptotic model approaches based on the linear combination of atomic orbitals (LCAO) and semiempirical (SE) methods for deriving couplings. It is found that FQ calculations compare best overall with the experiments, followed by the LCAO, and the SE approaches. The experimental results together with the theoretical calculations, allow us to investigate the effects on modeled spectra and derived abundances and their uncertainties arising from uncertainties in the MN rates. Numerical experiments in a large grid of 1D model atmospheres, and a smaller set of 3D models, indicate that neglect of MN can lead to abundance errors of up to 0.1 dex (26%) for Li at low metallicity, and 0.2 dex (58%) for Na at high metallicity, while the uncertainties in the relevant MN rates as constrained by experiments correspond to uncertainties in abundances of much less than 0.01 dex (2%). This agreement for simple atoms gives confidence in the FQ, LCAO, and SE model approaches to be able to predict MN with the accuracy required for non-LTE modeling in stellar atmospheres.

[en] In this paper we discuss the production of molecular PAH cations using an ECR ion source and their subsequent cooling studied with an electrostatic storage ring, the Mini-Ring on a time range up to 10 ms. We show that the ECR ion source can produce high currents of small PAH cation, here naphthalene and anthracene cations. Then, we report experimental result for the cooling of three PAH cations (anthracene, naphthalene and pyrene) stored in our compact electrostatic storage ring (the Mini-Ring). We show that the Poincaré recurrent fluorescence plays a major role in the cooling process of those PAH cations. We show that for a given internal energy, the cooling rate is much smaller for pyrene than for anthracene and naphthalene. We conclude that the Poincaré recurrent fluorescence is less efficient due to smaller oscillator strength of the D₂-D₀ electronic transition for pyrene.

[en] The interaction of 16 keV Cu⁻ ions with Al₂O₃ nano-capillaries of 50 nm diameter and 10 μm length was studied. The angular and charge state distributions of the transmitted particles were measured by a position-sensitive microchannel plate detector. It shows that transmitted particles appear as two peaks and consist of three charge states, Cu⁻, Cu⁰ and Cu⁺. As the tilt angle increases, more Cu⁻ ions lose electrons resulting in the formation of Cu⁰ and Cu⁺ during multiple collisions with the capillary walls. Unlike previously reported results on highly charged ions, keV-energy Cu⁻ ions undergo significant charge exchange processes with the inner walls of the capillaries. This indicates that the guiding effect is absent in the negative ion transmission under the very low ion current conditions.