As a further test of advanced theoretical methods to describe electron-impact single-ionization processes in complex atomic targets, we extended our recent work on $\mathrm{Ne}(2p$) ionization [X. Ren, S. Amami, O. Zatsarinny, T. Pfl\"uger, M. Weyland, W. Y. Baek, H. Rabus, K. Bartschat, D. Madison, and A. Dorn, Phys. Rev. A 91, 032707 (2015)] to $\mathrm{Ar}(3p$) ionization at the relatively low incident energy of ${E}_{0}=66$ eV. The experimental data were obtained with a reaction microscope, which can cover nearly the entire $4\ensuremath{\pi}$ solid angle for the secondary electron emission. We present experimental data for detection angles of 10, 15, and ${20}^{\ensuremath{\circ}}$ for the faster of the two outgoing electrons as a function of the detection angle of the secondary electron with energies of 3, 5, and 10 eV, respectively. Comparison with theoretical predictions from a $B$-spline $R$-matrix (BSR) with pseudostates approach and a three-body distorted-wave (3DW) approach, for detection of the secondary electron in three orthogonal planes as well as the entire solid angle, shows overall satisfactory agreement between experiment and the BSR results, whereas the 3DW approach faces difficulties in predicting some of the details of the angular distributions. These findings are different from our earlier work on $\mathrm{Ne}(2p$), where both the BSR and 3DW approaches yielded comparable levels of agreement with the experimental data.

We report a combined experimental and theoretical study on the electron-impact ionization of helium at E-0 = 70.6 eV and equal energy sharing of the two outgoing electrons (E-1 = E-2 = 23 eV), where a double-peak or dip structure in the binary region of the triple differential cross section is observed. The experimental cross sections are compared with results from convergent close-coupling (CCC), B-spline R-matrix-with-pseudostates (BSR), and time-dependent close-coupling (TDCC) calculations, as well as predictions from the dynamic screening three-Coulomb (DS3C) theory. Excellent agreement is obtained between experiment and the nonperturbative CCC, BSR, and TDCC theories, and good agreement is also found for the DS3C model. The data are further analyzed regarding contributions in particular coupling schemes for the spins of either the two outgoing electrons or one of the outgoing electrons and the 1s electron remaining in the residual ion. While both coupling schemes can be used to explain the observed double-peak structure in the cross section, the second one allows for the isolation of the exchange contribution between the incident projectile and the target. For different observation angles of the two outgoing electrons, we interpret the results as a propensity for distinguishing these two electrons-one being more likely the incident projectile and the other one being more likely ejected from the target.

The ionization and fragmentation of methane induced by low-energy (E0 = 66 eV) electron-impact is investigated using a reaction microscope. The momentum vectors of all three charged final state particles, two outgoing electrons, and one fragment ion, are detected in coincidence. Compared to the earlier study [Xu et al., J. Chem. Phys. 138, 134307 (2013)], considerable improvements to the instrumental mass and energy resolutions have been achieved. The fragment products CH4 (+), CH3 (+), CH2 (+), CH(+), and C(+) are clearly resolved. The binding energy resolution of ΔE = 2.0 eV is a factor of three better than in the earlier measurements. The fragmentation channels are investigated by measuring the ion kinetic energy distributions and the binding energy spectra. While being mostly in consistence with existing photoionization studies the results show differences including missing fragmentation channels and previously unseen channels.

We study the low-energy (E0 = 26 eV) electron-impact induced ionization and fragmentation of tetrahydrofuran using an (e, 2e + ion) method. The momentum vectors and, consequently, the kinetic energies for all three final-state charged particles are determined. The ionic fragments are clearly identified in the experiment with a mass resolution of one atomic mass unit. The fragmentation pathways of tetrahydrofuran are investigated by measuring the ion kinetic energy spectra and the binding energy spectra where a binding energy resolution of 1.5 eV has been achieved.

We present a new design of an advanced reaction microscope (REMI) for electron collisions with biologically relevant molecules. It will combine advancements which have been implemented for (e, 2e)-experiments, such as multi-hit detectors with a high detection efficiency, as well as new features for target creation and increased fragment acceptance.

We measured dissociative electron attachment in biologically relevant molecules using momentum imaging for negative ions in an apparatus that combines high resolutions of impact energy, fragment mass and fragment momentum. First investigations of the production of NH2−-ions around the A1 resonance at 5.7 eV impact energy show a clear dependence of the distribution of fragment dissociation angles on the projectile energy.

We study electron-impact induced dissociation of small argon clusters at a projectile energy of 120 eV. Kinetic-energy-release (KER) spectra for the final charge states 2Ar(+), Ar+ Ar2+ and Ar-2(+) + Ar+ of the Ar-2 and Ar-3 parent species and electron energies have been measured together with angular distributions of fragment ions. They are used to identify dissociation mechanisms such as Interatomic-Coulombic-Decay (ICD).

We present a combined experimental and theoretical study on the low-energy (E0 = 65 eV) electron- impact ionization of neon. The experimental data are compared to predictions from a hybrid second-order distorted-wave Born plus R-matrix approach (DWB2-RM), the distorted-wave Born approximation with inclusion of post-collision interaction (DWBA-PCI), a three-body distorted-wave approach (3DW), and a B-spline R-matrix (BSR) with pseudostates approach. Excellent agreement is found between experiment and the 3DW and BSR theories. The importance of PCI effects is clearly visible in this low-energy electron-impact ionization process.

We study electron-impact-induced dissociation of small van der Waals-bound argon complexes at a projectile energy of 120 eV. Kinetic-energy-release (KER) spectra of the Ar-2 and Ar-3 parent species for the final charge states 2Ar(+), Ar+ + Ar2+, and Ar2+ + Ar+ and electron energies have been measured together with angular distributions of fragment ions. They are used to identify dissociation mechanisms such as interatomic Coulombic decay (ICD).

We use an improved target recoil momentum spectroscopy setup to determine differential cross sections for excited metastable state production in atoms and molecules by electron impact and show its capabilities for an atomic helium target. A crossed beam setup with a supersonic helium jet and a pulsed electron beam at energies close to the excitation threshold of 19.82 eV was used. Measuring the recoil momentum vector of the target instead of the momentum of the scattered electron removes common restrictions to the accessible scattering angles while the microchannel plate detector ensures a high counting efficiency. Using a photoemission electron source we reach an energy resolution of about 200 meV at 1 µA peak current. Results are compared with simulations using theoretical convergent-close-coupling (CCC), R-matrix with pseudo-states (RMPS) and B-spline R-matrix (BSR) calculations and show good agreement.

We study the low energy electron impact-induced ionization and fragmentation of the tetrahydrofuran molecule using the reaction microscope. All three charged final state particles, two outgoing electrons and one fragment ion are detected in coincidence. The binding energy spectra and fully differential ionization cross sections for different fragment species are determined. As result detailed insight into the ionization mechanisms can be gained and track structure simulations for the investigation of radiation action can be supported.

We study the threshold excitation of metastable He*(1s2s 1,3S) states by combined electron impact and intense laser radiation (λ = 532 nm/1064 nm, I = 1010-1012W/cm2). A new experimental setup is used combining a ns-pulsed electron beam extracted from a photo-cathode, a single frequency Nd:YAG laser beam and a reaction microscope. Fully differential scattering cross sections are obtained by measuring the recoil momentum of the metastables.

As a fundamental test for state-of-the-art theoretical approaches, we have studied the single ionization (2p) of neon at a projectile energy of 100 eV. The experimental data were acquired using an advanced reaction microscope that benefits from high efficiency and a large solid-angle acceptance of almost 4π. We put special emphasis on the ability to measure internormalized triple-differential cross sections over a large part of the phase space. The data are compared to predictions from a second-order hybrid distorted-wave plus R-matrix model and a fully nonperturbative B-spline R-matrix (BSR) with pseudostates approach. For a target of this complexity and the low-energy regime, unprecedented agreement between experiment and the BSR model is found. This represents a significant step forward in the investigation of complex targets.

We present in this paper an (e, 2e + ion) investigation of the dissociative ionization of methane by 54 eV electron impact employing the advanced reaction microscope. By measuring two electrons and the ion in the final state in triple coincidence, the species of the ions are identified and the energies deposited into the target are determined. The species and the kinetic energies of the fragmented ion show strong dependence on the intermediate states of the parent ion. Possible decay pathways for the production of different species of ions are analyzed.