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We report on a joint experimental and theoretical study of photoelectron circular dichroism (PECD) in methyloxirane. By detecting O 1s-photoelectrons in coincidence with fragment ions, we deduce the molecule's orientation and photoelectron emission direction in the laboratory frame. Thereby, we retrieve a fourfold differential PECD clearly beyond 50%. This strong chiral asymmetry is reproduced by ab initio electronic structure calculations. Providing such a pronounced contrast makes PECD of fixed-in-space chiral molecules an even more sensitive tool for chiral recognition in the gas phase., Comment: 5 figures

When a strong laser pulse induces the ionization of an atom, momentum conservation dictates that the absorbed photons transfer their momentum to the electron and its parent ion. The sharing of the photon momentum between the two particles and its underlying mechanism in strong-field ionization, occurring when the bound electron tunnels through the barrier created by the superposition of the atomic potential and the electric laser field, are still debated in theory1–4 after 30 years of research. Corresponding experiments are very challenging due to the extremely small photon momentum and their precision has been too limited, so far, to ultimately resolve this debate5–8. By utilizing an experimental approach relying on two counter-propagating laser pulses, we present a detailed study of the effects of the photon momentum in strong-field ionization. The high precision of the method and the intrinsically known zero momentum allow us to unambiguously demonstrate the action of the light’s magnetic field on the electron while it is under the tunnel barrier, which has only been theoretically predicted so far1–3,9, thereby disproving opposing predictions5,10,11. Our results deepen the understanding of, for example, molecular imaging12,13 and time-resolved photoelectron holography14. Experiments with two counter-propagating laser beams report the observation that the photon momentum is shared between the electron and parent ion in strong-field ionization, which results from the photon’s magnetic field acting on the electron.

We investigate $K$-shell ionization of ${\mathrm{N}}_{2}$ at 40 keV photon energy. Using a cold target recoil ion momentum spectroscopy reaction microscope, we determine the vector momenta of the photoelectron, the Auger electron, and both ${\mathrm{N}}^{+}$ fragments. These fully differential data show that the dissociation process of the ${\mathrm{N}}_{2}^{2+}$ ion is significantly modified not only by the recoil momentum of the photoelectron but also by the photon momentum and the momentum of the emitted Auger electron. We find that the recoil energy introduced by the photon and the photoelectron momentum is partitioned with a ratio of approximately $30\ensuremath{\mathbin:}70$ between the Auger electron and fragment ion kinetic energies, respectively. We also observe that the photon momentum induces an additional rotation of the molecular ion.

Modern momentum imaging techniques allow for the investigation of complex molecules in the gas phase by detection of several fragment ions in coincidence. For these studies, it is of great importance that the single-particle detection efficiency e is as high as possible, as the overall efficiency scales with e over n, i.e. the power of the number of detected particles. Here we present measured absolute detection efficiencies for protons of several micro-channel plates (MCPs), including efficiency enhanced "funnel MCPs". Furthermore, the relative detection efficiency for two-, three-, four-, and five-body fragmentation of CHBrClF has been examined. The "funnel" MCPs exhibit an efficiency of approx. 90 percent, gaining a factor of 24 (as compared to "normal" MCPs) in case of a five-fold ion coincidence detection., 8 pages, 7 figues, submitted to Review of Scientific Instruments

We examine correlated electron and doubly charged ion momentum spectra from strong field double ionization of Neon employing intense elliptically polarized laser pulses. An ellipticity-dependent asymmetry of correlated electron and ion momentum distributions has been observed. Using a 3D semiclassical model, we demonstrate that our observations reflect the sub-cycle dynamics of the recollision process. Our work reveals a general physical picture for recollision-impact double ionization with elliptical polarization, and demonstrates the possibility of ultrafast control of the recollision dynamics., Comment: 6 pages, 5 figures

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.

Many-particle dynamics in atomic and molecular physics has been investigated by using the COLTRIMS reaction microscope. The COLTRIMS technique visualizes photon and ion induced many-particle fragmentation processes in the eV and milli-eV regime. It reveals the complete momentum pattern in atomic and molecular many-particle reactions comparable to the bubble chamber in nuclear physics.  2005 Elsevier B.V. All rights reserved.

The single ionization (SI) and the transfer ionization (TI) of H2 have been investigated utilizing the Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) reaction microscope. Continuum electron velocity spectra have been measured for experimentally determined nuclear motion. Electron velocity distributions for the SI of H2 show that the ejected electrons lie mainly in the scattering plane where their velocities were found to lie between those of the recoiling target and the scattered projectile. In addition to a group of electrons seen in SI saddle electrons group, the electron velocity spectra for TI of H2 unveiled the existence of another group of electrons with different structure. These electrons were emitted with velocities greater than the projectile velocity and found to result from a narrow range of impact parameters. These fast forward electrons reveal a substantial amount of out-of-plane scattering. 2005 Elsevier B.V. All rights reserved.

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 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.

This report will introduce the reader to the method of measuring electron and ion momentum distributions from fixed-in-space molecules using modified versions of the COLTRIMS technique. Following the introduction and a description of the working principles of this technique, a detailed discussion of the design of the electron and the ion detection part of the spectrometer will be presented. The actual measurement represents only a minor fraction of a COLTRIMS-like experiment. We therefore give an in-depth view at the basics of the offline-analysis for the field of detecting multiple particles from a Coulomb exploding molecule. Achievable resolutions, the possibilities of background suppression via multiparticle software coincidence methods, and the improvement of electron momentum resolution by center-of-mass-correction will be discussed, followed by an example of a setup for low energy electrons (

We study triple-ionization-induced, spatially asymmetric dissociation of ${\mathrm{N}}_{2}$ using angular streaking in an elliptically polarized laser pulse in conjunction with few-cycle pump-probe experiments. The kinetic-energy-release dependent directional asymmetry in the ion sum-momentum distribution reflects the internuclear distance dependence of the fragmentation mechanism. Our results show that for 5--35-fs near-infrared laser pulses with intensities reaching 10${}^{15}$ W/cm${}^{2}$, charge exchange between nuclei plays a minor role in the triple ionization of N${}_{2}$. We demonstrate that angular streaking provides a powerful tool for probing multielectron effects in strong-field dissociative ionization of small molecules.

Using the cold target recoil ion momentum spectroscopy (COLTRIMS) technique, we have measured the simultaneous projectile and target ionization in collisions of ${\mathrm{He}}^{+}$ projectiles with a mixture of gaseous ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ for an incident projectile energy of 650 keV. Motivated by Cooper et al. [Phys. Rev. Lett. 100, 043204 (2008)], we look for differences in the ionization cross section of the two isotopes with the highest resolution and statistical significance. Contributions of the electron-electron and electron-nucleus interactions have been clearly separated kinematically by measuring the longitudinal and transverse momentum of the recoiling ion. We find no significant isotope effect in any of our momentum distributions.

We investigate orientation effects in the fragmentation of He${}_{2}$ and ${\mathrm{Ne}}_{2}$ induced by ${S}^{14+}$ projectiles at an impact energy of 11.37 MeV/u. Multiple ionization shows a strong dependence on the orientation of the dimer axis with respect to the projectile beam axis. We attribute these effects to the impact-parameter-dependent ionization probability $P(b)$ for the atomic scattering process S${}^{14+}+\mathrm{He}$ and S${}^{14+}+\mathrm{Ne}$ and compare our data with a Monte Carlo simulation.

We present an experimental investigation into the angular and energy distributions of electrons set free by the interaction of hydrogen molecular ions with strong laser fields. The results extend on those presented previously [M. Odenweller et al., Phys. Rev. Lett. 107, 143004 (2011)] for circularly polarized light. Pulses of laser light ($\ensuremath{\lambda}=780$ nm, $I\ensuremath{\approx}6\ifmmode\times\else\texttimes\fi{}{10}^{14}$ W cm${}^{\ensuremath{-}2}$, $\ensuremath{\tau}\ensuremath{\approx}40$ fs) of both linear and circular polarization are focused onto an H${}_{2}$${}^{+}$ molecular ion beam. The momenta of the proton and electron fragments are determined in a coincidence experiment, enabling electron momentum emission patterns in the molecular frame to be deduced for specific values of internuclear distances.

We investigate the onset of photoionization shakeup induced interatomic Coulombic decay (ICD) in He2 at the He+*(n = 2) threshold by detecting two He+ ions in coincidence. We find this threshold to be shifted towards higher energies compared to the same threshold in the monomer. The shifted onset of ion pairs created by ICD is attributed to a recapture of the threshold photoelectron after the emission of the faster ICD electron., Comment: 5 Pages, 2 Figures

which show rich structures for ion scattering angles above 2 mrad arising dominantly from two-electron states. Our calculations reveal that minima in the measured distributions are zeroes in the electronic probability density resulting from vortices in the electronic current. PACS numbers: 34.50.Fa, 34.10.+x Molecular bonds are formed and broken in slow ion-atom collisions on a sub-femtosecond time scale. Upon bond breaking, the electrons forming the bond can be promoted to the continuum where the square of their wave function can be measured. A significant and unexpected electron dynamics in this process was predicted in the 1980

We study the order in which a strong laser field removes multiple electrons from a van der Waals (vdW) cluster. The N2Ar, with an equilibrium T-shaped geometry, contains both a covalent and a vdW bond and serves as a simple yet rich example. Interestingly, the fragmenting double and triple ionizations of N2Ar with vdW bond breaking are favored when the vdW bond is aligned along the laser field polarization vector. However, the orientation of the covalent bond with respect to the laser field rules the triple ionization when both the covalent and vdW bonds are simultaneously broken. Electron-localizationassisted enhanced ionization and molecular orbital profile-dominated, orientation-dependent ionization are discussed to reveal the order of electrons release from different sites of N2Ar. Strong laser fields effectively lead to multiple ionization of atoms, molecules, and clusters, which, in turn, results in multiple bond breakage, fragmentation, and Coulomb explosion. The microscopic mechanisms of this multiple laser matter interaction have mainly been studied in two size regimes: atoms and small linear molecules, for which the individual sequential ionization steps determine the physics, and extended systems, which are governed by collective effects. One key ingredient determining the order of ionization events is the binding energy, and a second is the geometry. As the size of the system increases, the ionization potentials for different orbitals and sites become more and more degenerate and the geometry plays an increasingly important role. Two elements of structure have been identified to govern strong field ionization. First, the shape of the orbital strongly influences the ionization probability. This is best established for molecules where the single ionization rate has been found to strongly depend on the angle between the polarization vector of the laser field and the molecular axis, as numerically predicted by the strong field approximation [1] and molecular Ammosov-Delone-Krainov tunneling rate [2], and experimentally demonstrated by probing the profiles [3–5] and the dipole moments [6 ]o f the ionizing orbitals. Second, the multiple ionization rate is found to be strongly enhanced for a molecule oriented along the laser field when the bond stretches to a critical length [7]. Under these conditions a localization of the charge on one site [8,9] and joint action of this charge center together with the light field boost the ionization probability, which is alternatively understood as the charge-resonance enhanced ionization [10,11]. This enhanced ionization scenario has been probed by the directional emission of the fragment ions [12], or the electron with respect to the field vector and molecular

We study the directional dissociative ionization of diatomic molecules (H2, N2, Ar2, and CO) by intense phase-controlled elliptically polarized two-color pulses. The phase between the two colors of our elliptically polarized two-color pulse is unambiguously and straightforwardly assigned by tracing the momentum of the released electron, streaked by the rotating laser field, which is imprinted in the momentum of the correlated ion. The laser-driven electron motion, electron-localization-assisted enhanced multielectron ionization, and role of the orbital shape for the asymmetric dissociative ionizations of various molecules are discussed.

We investigate the contribution of interatomic Coulombic decay induced by ion impact in neon and argon dimers (Ne${}_{2}$ and Ar${}_{2}$) to the production of low-energy electrons. Our experiments cover a broad range of perturbation strengths and reaction channels. We use 11.37 MeV/u S${}^{14+}$, 0.125 MeV/u He${}^{1+}$, 0.1625 MeV/u He${}^{1+}$, and 0.150 MeV/u He${}^{2+}$ as projectiles and study ionization, single and double electron transfer to the projectile, as well as projectile electron loss processes. The application of a COLTRIMS reaction microscope enables us to retrieve the three-dimensional momentum vectors of the ion pairs of the fragmenting dimer into Ne${}^{q+}$-Ne${}^{1+}$ and Ar${}^{q+}$-Ar${}^{1+}$ ($q=$ 1, 2, 3) in coincidence with at least one emitted electron.

The detailed theoretical and experimental analysis of the angular distributions of electrons from interatomic Coulombic decay (ICD) of the Ne dimer in the molecular frame is performed. In the initial state the doubly charged dimer ion has one $2s$ vacancy and one $2p$ vacancy on one atom. After the ICD process the neutral neon atom is ionized and the triply charged molecular ion dissociates into singly and doubly charged atomic ions, ${\text{Ne}}^{2+}(2{p}^{\ensuremath{-}2})+{\text{Ne}}^{+}(2{p}^{\ensuremath{-}1})$. From the coincident measurement of kinetic energy release (KER) of the ions and the ICD electron the decay channel can be identified unambiguously. The most detailed experimental data have been obtained for the singlet dicationic state Ne${}^{2+}(2{p}^{\ensuremath{-}2}){[}^{1}\phantom{\rule{-0.16em}{0ex}}D]$. Different KER energies correspond to different internuclear distances at which the ICD process takes place. In experiment the data have been presented for three regions of KER energies, and the corresponding calculations have been performed for three fixed internuclear distances. In calculations we imply that all the electrons in Ne${}_{2}$ to a good approximation are localized. However, we need to retain the molecular character of the dimer wave functions which opens the possibility for the ICD process. To do it, we calculate at first the Hartree-Fock ground state wave functions of the neutral Ne${}_{2}$ dimer using the standard procedure for homonuclear diatomic molecules corresponding to the ${D}_{\ensuremath{\infty}h}$ symmetry group. For the doubly charged ion Ne${}_{2}{}^{2+}$ with two vacancies on one atom the symmetry is lowered to ${C}_{\ensuremath{\infty}v}$, and we are looking now for the set of one-electron Hartree-Fock wave functions which are localized either on the left or on the right atom as a linear combination of symmetry-adopted wave functions. The theory correctly reproduces the experimental data and predicts the sharp variation of the angular distributions as a function of internuclear distance.

We coincidently measure the molecular frame photoelectron angular distribution and the ion sum-momentum distribution of single and double ionization of CO molecules by using circularly and elliptically polarized femtosecond laser pulses, respectively. The orientation dependent ionization rates for various kinetic energy releases allow us to individually identify the ionizations of multiple orbitals, ranging from the highest occupied to the next two lower-lying molecular orbitals for various channels observed in our experiments. Not only the emission of a single electron, but also the sequential tunneling dynamics of two electrons from multiple orbitals are traced step by step. Our results confirm that the shape of the ionizing orbitals determine the strong laser field tunneling ionization in the CO molecule, whereas the linear Stark effect plays a minor role., This paper has been accepted for publication by Physical Review Letters

We measure the angular distribution of an electron emitted by a strong elliptically polarized two-color laser field from exploding doubly charged molecular nitrogen. This angular distribution is vastly different for emission of the electron from the up-field core of the molecule as compared to that from the down-field core. The emission from the down-field core leads to a slight rotation with respect to the internuclear axis in the direction expected by the Coulomb effect of the remaining ion, while, for the emission from the up-field core, this direction is inversed. Our semiclassical simulations suggest that this unexpected angular distribution is caused by an initial longitudinal momentum of the electron freed by over-the-barrier ionization above the inner barrier in the molecule. The initial kinetic energy is in the range of the potential energy of the Stark-shifted orbital above the barrier.

We have studied electron emission from the ${\mathrm{H}}_{2}^{+}$ ion by a circularly polarized laser pulse (800 nm, $6\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$). The electron momentum distribution in the body fixed frame of the molecule is experimentally obtained by a coincident detection of electrons and protons. The data are compared to a solution of the time-dependent Schr\"odinger equation in two dimensions. We find radial and angular distributions which are at odds with the quasistatic enhanced ionization model. The unexpected momentum distribution is traced back to a complex laser-driven electron dynamics inside the molecule influencing the instant of ionization and the initial momentum of the electron.

Using a fully correlated, four-dimensional lattice, time-dependent Schr\"odinger equation model of the collisions of bare projectile ions with two-electron atoms (H${}^{+}$, He${}^{2+}$ $+$ He), we demonstrate the existence of vortices in the resulting spectrum of ejected electrons. Following the uncovering of these features in collisions involving only one electron (H${}^{+}$ $+$ H) [Macek et al., Phys. Rev. Lett. 102, 143201 (2009)], this demonstration provides impetus for seeking these features in more readily feasible experimental conditions using a cold helium target and the reaction microscope technique.

We observe multiply frustrated tunneling ionization-induced dissociation of the argon dimers by intense linearly polarized ultrashort laser pulses. By measuring the kinetic energy release and angular distribution of the Coulomb explosion of up to eightfold ionized argon dimers, we can trace the recapture of up to two electrons to Rydberg states of the highly charged compound at the end of the laser pulse. Upon dissociation of the dimer, the Rydberg electron prefers to localize at the atomic ion with the higher charge state. We probe the electron recapture dynamics by a time-delayed weak pulse.

Theoretical two-center interference patterns produced (i) by the $K$-shell photoionization process of the ${\mathrm{N}}_{2}$ molecule and (ii) by the Auger decay process of the $K$-shell hole state of the ${\mathrm{N}}_{2}$ molecule are compared for the case of equal photo- and Auger-electron energies of about 360 eV. The comparison shows that both the angular distribution of the photoelectrons and the angular distribution of the Auger electrons of equal energy in the molecular frame are primarily defined by the Young interference. The experimental data for the angular resolved $K$-shell Auger electrons as a function of the kinetic-energy release (KER) obtained earlier [Phys. Rev. A 81, 043426 (2010)] have been renormalized in order to visualize the angular variation in the regions of low Auger-electron intensities. That renormalized data are compared with the corresponding theoretical results. From the known behavior of the potential energy curves, the connection between the KER and the internuclear distance can be established. Since the Young interference pattern is sensitive to the internuclear distance in the molecule, from the measured KER dependence of the Young interference pattern one can trace the behavior of the Auger-electron angular distribution for different molecular terms as a function of internuclear distance. The results of that analysis are in a good agreement with the corresponding theoretical predictions.

Fragmentation of highly charged molecular ions or clusters consisting of more than two atoms can proceed in a one step synchronous manner where all bonds break simultaneously or sequentially by emitting one ion after the other. We separated these decay channels for the fragmentation of CO(2)(3+) ions by measuring the momenta of the ionic fragments. We show that the total energy deposited in the molecular ion is a control parameter which switches between three distinct fragmentation pathways: the sequential fragmentation in which the emission of an O(+) ion leaves a rotating CO(2+) ion behind that fragments after a time delay, the Coulomb explosion and an in-between fragmentation--the asynchronous dissociation. These mechanisms are directly distinguishable in Dalitz plots and Newton diagrams of the fragment momenta. The CO(2)(3+) ions are produced by multiple electron capture in collisions with 3.2 keV/u Ar(8+) ions.

Using the cold target recoil ion momentum spectroscopy technique, we have measured state-selective projectile scattering angles for single and double electron captures in collisions of protons and ${\text{He}}^{1,2+}$ projectiles with a helium target for incident energies of 60--630 keV/u. We also report theoretical results obtained by means of four-body one-channel distorted-wave models (continuum distorted-wave Born final state, continuum distorted-wave Born initial state, and Born distorted wave) and find mixed agreement with the measured data.

We used cold target recoil ion momentum spectroscopy for a comprehensive study of the decay of a neon dimer $({\mathrm{Ne}}_{2})$ after removal of a $1s$ electron from one of the atoms of the dimer. Multiple decay pathways are found and identified, mostly being connected to different types of interatomic Coulombic decay (ICD) such as the ``direct'' ICD which happens via the transfer of a virtual photon, the ``exchange'' ICD via an electron transfer and the electron transfer mediated decay. A quantitative theoretical analysis of these decay processes can be found in the preceding paper by Demekhin et al. [Phys. Rev. A 78, 043421 (2008)], as well as in Stoychev et al. [J. Chem. Phys. 129, 074307 (2008)].

The dissociative electron transfer from He into 10 keV H2+ was measured in a kinematically complete experiment by using the cold target recoil ion momentum spectroscopy imaging technique in combination with a highly resolving molecular fragment imaging technique. The electron transfer into the dissociative b(3)Sigma+_(u) state of H2 could be selected by kinematic conditions. We find a striking double slit interference pattern in the transverse momentum transfer which we can modify by selecting different internuclear distances. Compared to an optical double slit, interference minima and maxima are interchanged. The latter is the result of a phase shift in the electronic part of the wave function.

We used Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) to investigate the decay of Ne$_2$ after K-shell photoionization. The breakup into Ne$^{1+}$ / Ne$^{2+}$ shows interatomic Coulombic decay (ICD) occurring after a preceding atomic Auger decay. The molecular frame angular distributions of the photoelectron and the ICD electron show distinct, asymmetric features, which imply localization of the K-vacancy created at one of the two atomic sites of the Ne$_2$ and an emission of the ICD electron from a localized site. The experimental results are supported by calculations in frozen core Hartree-Fock approach., Comment: 4 pages, 4 figures

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.

We use intense femtosecond laser pulses to multiply ionize and directly image the structures of N(2)Ar, O(2)Ar, and O(2)Xe dimers by coincidently measuring the momenta of the fragment ions. All these dimers are found to have an equilibrium T-shaped structure in which the bond of the diatomic molecule is perpendicular to the dimer axis. The equilibrium distance between the rare-gas atom and the center-of-mass of the diatomic molecule is estimated to be R(N2-Ar) ~ 3.86 Å, R(O2-Ar) ~ 3.65 Å, and R(O2-Xe) ~ 4.07 Å, respectively. For the T-shaped N(2)Ar dimer, both sequential and direct triple-ionization-induced three-body breakups are observed. In contrast to N(2)Ar dimer, other structures are found to coexist with the dominating T-shaped one for O(2)Ar and O(2)Xe.

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.