[en] Initiated by some discrepancies between beam and laser-induced fluorescense experiments, the N⁺ + CO charge transfer reaction has been explored in a guided beam apparatus. In a modified arrangement it is now possible to reach even subthermal energies and to detect product ions above 6 meV without discrimination. The test to prove this, based on a time of flight analysis, will be discribed. These exceptional experimental conditions allow to expand the measurement of the integral cross section down to 20 meV. By analysis of the product velocities, the forward / backward ratio has been determined. The results indicate, that two mechanisms are operative: an electron transfer, followed by the formation of a strongly coupled complex and an electron transfer without essential interaction of tse nuclei. The consequences for a LIF experiment will be discussed briefly. (Author)

[en] Reactions of methane cations, CH₄⁺, with H₂, HD and D₂ have been studied in a variable temperature 22-pole ion trap from room temperature down to 15 K. The formation of CH₅⁺ in collisions with H₂ is slow at 300 K, but it becomes faster by at least one order of magnitude when the temperature is lowered to 15 K. This behavior is tentatively explained with a longer complex lifetime at low temperatures. However, since tunneling is most probably not responsible for product formation, other dynamical or statistical restrictions must be responsible for the negative temperature dependence. In collisions of CH₄⁺ with HD, the CH₅⁺ product ion (68% at 15 K) prevails over CH₄D⁺ (32%). Reaction of CH₄⁺ with D₂ is found to be much slower than with H₂ or HD. The rate coefficient for converting CH₄⁺ into CH₃D⁺ by H-D exchange has been determined to be smaller than 10^-12 cm³/s, indicating that scrambling in the CH₆⁺ complex is very unlikely

[en] This report summarizes recent advances in using innovative storage devices based on inhomogeneous, time-dependent electric fields. Electrode arrangements include quadrupoles, linear octopoles, higher-order multipoles, or a series of ring electrodes. Applying suitable oscillating voltages to such structures, with frequencies ranging from GHz via MHz to a few Hz, a variety of charged particles can be confined ranging from electrons via molecular ions to nanoparticles with masses of more than 10¹⁰ u. This contribution give a short summary of the theory, especially the effective potential approximation. The features of the technique are illustrated by several examples such as trapped ion beams, buffer gas cooling of ions in a 22-pole trap, and nanoparticle mass spectrometry in a quadrupole. Recent experimental results include growth of structures, isotope enrichment, and submonolayer gas ad- and desorption on a stored 500 nm SiO₂ particle. In the summary a few hints concerning ongoing experiments are given such as laser induced reactions, combination of traps with atomic beams, state-selected perturbation of a trapped low temperature ensemble with an infrared laser, and future trends in nanoparticle research.

[en] This report is concerned with recent advances in the application of the guided beam method and presents new results for some reactions and charge transfer processes (C⁺ + H₂, N⁺ + CO, Ar⁺ + O₂ and CO, and Ar⁺⁺ + He). Experimental progress involves the preparation of ion beams in the 'sub - 0.1 eV range', the precise calibration of their kinetic energy and the determination of product velocities in an octopole. The successful combination of this technique with others (like photoionization or photon - ion coincidences) will be briefly mentioned. The above choice of reaction systems allows a comparison with other methods (SIFT, DRIFT, ICR, LIF and crossed beams). (Auth.)

[en] The proton deuteron exchange reactions of H⁺+D₂, D⁺+H₂, H⁺+HD, and D⁺+HD have been studied using a recently developed dynamically biased statistical theory. Above 0.5 eV, complex formation and decay probabilities have been defined with the help of trajectories, calculated on a DIM energy surface. At lower kinetic energies, the induced dipole and quadrupole interaction has been taken into account. The cross sections and thermal rate coefficients are in reasonable agreement with experimental values measured with different techniques. (Auth.)

[en] This contribution concentrates on the use of an ion trapping technique which has been developed for studying collision processes and chemical reactions at low temperatures and which utilizes inhomogeneous radio frequency fields. Special emphasis is put onto recent progress achieved with a cryo cooled 22-pole ion trap. Experimental results, measured at a nominal temperature of 10K, are presented for radiative association of CH₃⁺ and C₂H₂⁺ with H₂. Another group of results discussed in this paper deals with the dynamics of the growth of hydrogen clusters starting from H₃⁺. In all cases, the influence of H₂ rotation was examined by utilizing p-H₂ and n-H₂. Also the process of isotope fractionation in the presence of HD and D₂ is briefly mentioned

[en] Relative three-body association rate coefficients for the title reaction have been measured as a function of the rotational state j of the CO⁺ ion at collision energies below 1 meV. A significant decrease of the dimer formation has been observed when j increases from 0 to 7 (E_rot=0-13.7 meV). Multiphoton ionization (MPI) is used to create the ions in the high pressure region of a pulsed supersonic expansion of pure CO. This method allows both the rather precise determination of the rotational population of the neutrals (< E_rot>∝1.5 meV) and the preparation of the ions exclusively in the vibrational ground state and in well defined rotational states. Due to its very steep energy dependence the ternary association reaction can be 'switched off' within a few tenths of a millimeter using an acceleration field of 1-3 V/cm. The short effective interaction time of less than 250 ns leads to almost single collision conditions, i.e. we perform state selective studies. The kinetics and kinematics (mean kinetic energy, competition between relaxation and association) are analyzed numerically. A consistent picture results from the assumption that the ternary rate coefficient depends only on the total energy of the complex irrespective of whether its origin is rotation or translation. (orig.)

[en] The reaction N⁺ + O₂ → NO⁺ + O has been studied at collision energies between 0.35 eV and 10 eV using a guided beam differential scattering apparatus. Above 3 eV, we find scattering diagrams, characteristic of a direct process and a tendency to convert translational energy into internal excitation. This is in excellent agreement with former beam experiments (Tully et al. (5)). Some structures in the velocity distributions appear in outlies. A sharp cutoff at ΔEsub(t) < -4.2 eV (lowest three body channel) indicates that dissociation of the NO⁺ occurs only if the O atom is in its ground state and that there is a propensity to transfer most of the available energy into the NO⁺ products. Below 3 eV an other reaction mechanism becomes dominant, the angular distributions spread out and the kinetic energy release inreases. At 0.35 eV about 30% of the exothermicity appears as translational energy. This result agrees satisfactory with recently measured visible and infrared chemiluminescence data. (Author)

[en] Short communication

[en] Formation of stable CH5(+) and CD5(+) has been studied in a liquid nitrogen cooled radio-frequency (RF) ion trap. Ternary rate coefficients, k3, have been measured for He, H2, and D2 as the stabilizing collision partner. The results for He are in satisfying agreement with SIFT data. The experiments have been performed at very low densities permitting information to be extracted on the radiative association process. Because both k3 and the radiative rate coefficient k(r) are observed under the same experimental conditions, comparison leads to a reliable upper limit of the radiative stabilizing rate of the intermediate CH5(+) collision complex. The results are significantly smaller than the values currently discussed in the literature, but they are in accord with infrared relaxation rates measured directly for highly excited CH5(+) ions. Using two different mixtures of p-H2 and o-H2 at 80 K, the influence of the H2 rotational energy was determined. The derived ratio is four times smaller than predicted from theoretical work. 30 refs