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Synopsis The installation of a reaction microscope (COLTRIMS [1]) in the electrostatic Frankfurt Low Energy Storage Ring (FLSR) [2] has been completed. A first experiment, exploring the KER for dissociative electron transfer to HeH+ ions at 20 keV from a cold supersonic He gas target have been carried. Even at the moderate vacuum of 10−8 mbar a change of the KER and the Q value distribution due to cooling of the molecular ions during the storage time can be observed. In this contribution the final experiment, performed after heating the ring will be discussed.

We have used the cold target recoil ion momentum spectroscopy imaging technique to investigate dissociative ionization of H2 by 25 keV proton impact. A kinematically complete picture of the dissociative ionization dynamics for slow proton collision has been obtained. The results show a strong impactparameter dependence of the fragmentation process of H2. This clearly emerged in the energy distributions of the H + ions generated for different impact parameters. At large impact parameters the H + ions equally share the energy liberated in the collision whereas at small impact parameters, the energy sharing is quite asymmetric. We also observed a strong dependence of the electron emission on molecular alignment. The momentum distribution of the emitted electron generated for a fixed-in-space H2 molecule displays that the electrons are more likely to be emitted perpendicular to the molecular axis.

The zero-degree ejected-electron spectrum for protons incident on He at 25 keV is examined experimentally using the COLTRIMS technique. The momentum distribution of the emitted electrons for the transfer ionization (TI) reaction channel is measured in coincidence with the momentum vectors of the recoil ion and the scattered projectile. The momentum distribution of the electrons emitted around zero degree in the forward direction for the TI reaction channel shows two prominent structures: the electron-capture-to-the-continuum (ECC) peak and the saddle-point peak. From the measured fully differential electron emission cross sections with respect to the scattering plane we can deduce that the main ECC formation mechanism is electron promotion via quasimolecular orbitals.

A joint theoretical–experimental study of the transfer ionization process p+H e→ H 0 +H e 2+ +e − is presented. For the first time all particles in the final state have been detected in triple coincidence. This fully differential measurement is in good agreement with a theoretical model where the target is described by a wavefunction containing both radial and angular correlation terms.

We present a joint experimental and theoretical study of the gerade and ungerade amplitudes of the photo double ionization of helium at excess energies of 100 eV and 450 eV above the threshold. We describe a method of extracting the amplitudes from a COLTRIMS data set. The experimental results are well reproduced by convergent close-coupling (CCC) calculations. The fully differential cross section data underlying this study can be found in our companion papers immediately preceding this one.

We present a joint experimental and theoretical study for the fully differential cross section of the photo double ionization (PDI) of helium with linearly polarized light at the excess energies Eexc = 100 eV and 450 eV above the threshold. The fully differential cross section is obtained by measuring the three-dimensional momentum vectors of one electron and the He 2+ ion in coincidence using the COLTRIMS method. We give an overview of the momentum distribution of the three-body continuum 100 eV above the threshold. We show angular distributions for both electrons for various energy sharings at Eexc = 100 eV and 450 eV. The experimental results are well reproduced by a set of convergent close-coupling (CCC) calculations.

We present a joint experimental and theoretical study of the double differential cross section for the double ionization of helium by absorption of one 179 eV linear polarized photon (100 eV above threshold). We show the energy sharing and the asymmetry parameters in both single-particle coordinates and in Jacobi coordinates. An asymmetric sharing of the electron excess energy and a breakup of the electron pair preferentially parallel to the polarization axis is found. This marks a deviation from the propensity rule favouring perpendicular relative electron motion which has been observed to hold at energies closer to the double-ionization threshold.

Frankfurt low-energy storage ring (FLSR) is an electrostatic storage ring for low-energy ions up to q ·80 keV (q being the ion charge state) at Institut fur Kernphysik der Goethe-Universitat, Frankfurt am Main, Germany. It has especially been designed to provide a basis for experiments on the dynamics of ionic and molecular collisions in complete kinematics, as well as for high precision and time resolved laser spectroscopy. The ring has ‘racetrack’ geometry with a circumference of 14.23 m. It comprises four experimental/diagnostic sections with regions of enhanced ion density (interaction regions). First beam has successfully been stored in FLSR in summer 2013. Since then the performance of the ring has continuously been improved and an electron target for experiments on dissociative recombination has been installed in one of the experimental sections.

FLSR has been designed for experiments on the dynamics of atomic and molecular collisions. After successful commissioning, an experiment on the dissociative recombination of 4HeH+ has been started.

The validity of the Born series expansion for the charge transfer reactions is studied in the case of a proton-helium collision. Three dierent channels are considered, namely the charge transfer, transfer excitation and transfer ionization. The dierential cross sections and the contributions from dierent charge transfer mechanisms within various Born approximations are compared with experimental data. The role of the electron-electron correlations in the initial helium state is discussed in detail. It is shown that the rst Born approximation is valid in the case of reactions under consideration, provided very small scattering angles are involved and the proton energy is >500 keV. It is also shown that the electron-electron correlations in the initial helium state are important only in transfer excitation and transfer ionization reactions.

It's well known for atomic targets that the ionization in transfer ionization originates from electron knock-off or initial state correlated shake-off. For H2 molecules we have observed a similar behavior and additionally a dependency of the electron emission from the internuclear axis

2D distribution of momentum components of the ejected electron in the reaction H+ +He → H+He2++e at 630 keV proton is studied both theoretically and experimentally. This allows to unambiguously identify contributions from the shake-off and binary encounter mechanisms of transfer ionization. It is shown that the results are highly sensitive to the quality of the initial-state wave function.

Fully differential cross section (FDCS) for the transfer excitation (H+ + He ? H+He+*) at high proton energies (630 ? 1200 keV) is studied both experimentally and theoretically within the simplest Plane Wave First Born Approximation (PWFBA). The role of angular correlations in a trial helium ground state wave function is demonstrated.

The Helium Dimer (4He2), being the largest and most weakly bound diatomic molecule, is a unique system for probing quantum mechanical properties. Recent Experiments did first steps towards measuring the distribution of internuclear distances of the dimer. These measurements, however, only yielded a subset of bond length appearing in the ground state of the Helium dimer. Here we used cold target recoil ion momentum spectroscopy (COLTRIMS) and a femtosecond laser to map its complete vibrational wavefunction and gather the distribution of bond lengths in a much larger range.

We have developed a photon counting detector system for combined neutron and gamma radiography which can determine position, time and intensity of a secondary photon flash created by a high-energy particle or photon within a scintillator screen. The system is based on a micro-channel plate photomultiplier concept utilizing image charge coupling to a position- and time-sensitive read-out anode placed outside the vacuum tube in air, aided by a standard photomultiplier and very fast pulse-height analyzing electronics. Due to the low dead time of all system components it can cope with the high throughput demands of a proposed combined fast neutron and dual discrete energy gamma radiography method (FNDDER). We show tests with different types of delay-line read-out anodes and present a novel pulse-height-to-time converter circuit with its potential to discriminate gamma energies for the projected FNDDER devices for an automated cargo container inspection system (ACCIS)., Proceedings of FNDA 2011

In this paper, we shed new light on the molecular photoionization of a diatomic molecule. We will elaborate the differences and analogy between a quantum optical and light?matter interaction approach in a study of K-shell photoionization of N2 in which the photoelectron and the subsequently emitted Auger electron are both measured in coincidence in the body fixed frame of the molecule. The two electrons form an entangled state inside a double slit. By changing the photon energy we create different types of interference in the photoelectron and the Auger electron wave.

By using the COLd Target Recoil Ion Momentum Spectroscopy (COLTRIMS) we have investigated the 1s photoionization of neon dimers. Interatomic Coulombic Decay (ICD) takes place in the asymmetric charge breakup Ne2+/Ne1+. This breakup is used to determine whether the inner shell vacancies, resulting out of the photoionization of the dimer, and the valence shell vacancies, resulting out of the ICD, are localized at one of the atoms or delocalized over the two equivalent sites of the neon dimer.

With photon energies 10 eV above the K-edge the 1s photoionization of neon dimers was measured by using COLd Target Recoil Ion Momentum Spectroscopy. All decay channels resulting in the breakup Ne+ + Ne+ and Ne2+ + Ne+were identified. The latter was used to investigate the localization or delocalization of vacancies in the homonuclear diatomic system.

We employed the COLTRIMS (cold target recoil ion momentum spectroscopy) technique to investigate the collision of alpha particles with an energy of 150kev/u and he lium dimers (He2).

The possibility to separate Auger transitions to different repulsive doubly charged final ion states by measuring the photo- and the Auger -electrons in coincidence in the molecular frame is demonstrated.

The dissociative electron transfer from He into 10 keV H+2 was measured in a kinematically complete experiment. For electron transfer into the dissociative b3?+u state of H2 we find a striking double slit interference pattern in the transverse momentum transfer which we can modify by selecting different internuclear distances of the hydrogen molecule. Compared to an optical double slit, interference minima and maxima are interchanged.

The three-body break up of CO23+ has been investigated in a kinematically complete experiment. We are able to separate various dissociation pathways like synchronous, asynchronous and sequential fragmentation. We find that the various mechanism correlate to distinct excitation energies of the CO23+.

Coincident measurement of the Auger electron and fragment ion momenta emitted after carbon core-level photoionization of acetylene has yielded new understanding of how the dication fragments. Ab initio calculations and experimental data, including body-frame Auger angular distributions, are used to identify the parent electronic states and together yield a comprehensive map of the dissociation pathways which include surface crossings and barriers to direct dissociation. The Auger angular distributions for certain breakup channels show evidence of core–hole localization. (Some figures in this article are in colour only in the electronic version)