We describe the design of a novel type of storage device currently under construction at Stockholm University, Sweden, using purely electrostatic focussing and deflection elements, in which ion beams of opposite charges are confined under extreme high vacuum cryogenic conditions in separate "rings" and merged over a common straight section. The construction of this double electrostatic ion ring experiment uniquely allows for studies of interactions between cations and anions at low and well-defined internal temperatures and centre-of-mass collision energies down to about 10 K and 10 meV, respectively. Position sensitive multi-hit detector systems have been extensively tested and proven to work in cryogenic environments and these will be used to measure correlations between reaction products in, for example, electron-transfer processes. The technical advantages of using purely electrostatic ion storage devices over magnetic ones are many, but the most relevant are: electrostatic elements which are more compact and easier to construct; remanent fields, hysteresis, and eddy-currents, which are of concern in magnetic devices, are no longer relevant; and electrical fields required to control the orbit of the ions are not only much easier to create and control than the corresponding magnetic fields, they also set no upper mass limit on the ions that can be stored. These technical differences are a boon to new areas of fundamental experimental research, not only in atomic and molecular physics but also in the boundaries of these fields with chemistry and biology. For examples, studies of interactions with internally cold molecular ions will be particular useful for applications in astrophysics, while studies of solvated ionic clusters will be of relevance to aeronomy and biology.

Direct evidence of the interference effect in the electron emission spectra from ionization of molecular hydrogen in collisions with bare C and F ions at relatively low collision energies is presented. Oscillations due to the interference are deduced by comparing the measured double differential cross sections of the electrons emitted from molecular hydrogen to those emitted from atomic hydrogen, rather than using the calculated cross sections for H as in a previous report. We believe these experimental data provide stronger support for the evidence of the interference effect. We show that it is not only a feature of very high energy collisions, but also a feature to be observed in relatively lower energy collisions.

We present a novel experimental tool allowing for kinematically complete studies of break-up processes of laser-cooled atoms. This apparatus, the 'MOTReMi,' is a combination of a magneto-optical trap (MOT) and a reaction microscope (ReMi). Operated in an ion-storage ring, the new setup enables us to study the dynamics in swift ion-atom collisions on an unprecedented level of precision and detail. In the inaugural experiment on collisions with 1.5  MeV/amu O(8+)-Li the pure ionization of the valence electron as well as the ionization-excitation of the lithium target was investigated.

We use the forward-backward angular asymmetry in the electron emission cross sections in fast ion impact ionization of H 2 as a probe of the inversion symmetric coherence in homonuclear diatomic molecules. The electron energy dependence of the asymmetry parameter for H 2 exhibits oscillatory structure due to Young-type interference in contrast to atomic targets such as He. The asymmetry parameter technique provides a selfnormalized method to reveal the interference oscillation independent of theoretical models and complementary measurements on atomic H target. Angular distribution of various types of radiations ͑particles and photons͒ is known to be quite sensitive to various effects associated with different physical processes in atomic, nuclear, plasma physics and other branches of physics. In fast ion-atom ionization, the long range Coulomb interaction of the final state electrons with the target and the projectile ions influences the evolution of the electron wave function and thereby the angular distribution of electron emission. Such two-center effect is known to cause a large forward-backward asymmetry ͓1-4͔ in the electron emission spectrum. The electron emission spectrum from the simplest diatomic molecule H 2 manifests yet another important aspect of interference ͓5͔ in ion-atom ionization besides the wellknown mechanisms such as soft collision, two-center effect and binary encounter ͓1-4,6-8͔. Since the two indistinguishable H atoms in the H 2 molecule may be considered as the coherent emission sources of phase coupled electrons in a large impact parameter collision, their contributions add coherently and an interference effect should be observed. Therefore, the electron emission from H 2 may be viewed as a natural coherent system which is similar to Young's double slit interference phenomenon ͓5͔. We demonstrate here that the additional mechanism of Young-type interference plays a major role in the angular asymmetry of electron double differential cross section ͑DDCS͒ and asymmetry parameter itself would be a sensitive test to study the interference for a diatomic molecular target.Following the initial theoretical studies on the interference effect in electron scattering ͓9͔ and photoionization ͓5͔, very recently the evidence of Young-type interference was found in the fast-ion collisions with H 2 ͓10-12͔. Ideally one would have expected an oscillation in the DDCS spectrum due to interference. But a steep fall of the DDCS by about four or five orders of magnitude ͑see below͒ does not allow one to observe the oscillation directly. The oscillations, thereby, were observed in the DDCS ratios ͑H 2 -to-2H͒ which was explained due to the interference. However, the experiments using H are rare due to the experimental constraint and oscillations in the DDCS ratios were observed ͓4,12͔ in such experiment with H. Theoretical DDCS for atomic, or effective atomic H have also been employed ͓10,11͔ in the absence of an atomic H target. In such cases, the shapes of the oscillations are sensitive to the atomic parame...

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A reaction microscope (ReMi) has been combined with a magneto-optical trap (MOT) for the kinematically complete investigation of atomic break-up processes. With the novel MOTReMi apparatus, the momentum vectors of the fragments of laser-cooled and state-prepared lithium atoms are measured in coincidence and over the full solid angle. The first successful implementation of a MOTReMi could be realized due to an optimized design of the present setup, a nonstandard operation of the MOT, and by employing a switching cycle with alternating measuring and trapping periods. The very low target temperature in the MOT (∼ 2 mK) allow for an excellent momentum resolution. Optical preparation of the target atoms in the excited Li 2 2 P 3/2 state was demonstrated providing an atomic polarization of close to 100 %. While first experimental results were reported earlier, in this work we focus on the technical description of the setup and its performance in commissioning experiments involving target ionization in 266 nm laser pulses and in collisions with projectile ions.

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