Table of contents

Among amino acids, cysteine has been widely studied, becoming a standard for molecular self-assembly experiments, because its mercapto group (-SH) allows the formation of self-assembled monolayers (SAMs) on metal surfaces. Dissociative electron attachment (DEA) on L-cysteine SAMs is investigated utilizing a time-of-flight mass spectrometer coupled with a low-energy electron gun. The results show that electrons with kinetic energies of 3 to 15 eV attach to L-cysteine producing anionic fragments of different masses (e.g., H^-, O^-, OH^-, S^-, SH^-) via dissociation of intermediate transient anions. The anion yield functions exhibited purely resonant behaviour with electron energies below 15 eV, indicating that the formation of transient anions is the predominant mechanism of production of anionic fragments from L-cysteine dissociation.

We present negative ion formation from collisions of 100 eV neutral potassium atoms with acetic acid (CH₃COOH) and its deuterated analogue molecules (CH₃COOD, CD₃COOH). From the negative ion time-of-flight (TOF) mass spectra, OH^- is the main fragment detected accounting on average for more than 25% of the total anion yield. The complex internal rearrangement processes triggered by electron transfer to acetic acid have been evaluated with the help of theoretical calculations at the DFT levels explaining the fragmentation channel yielding OH^-.

We analyze the two-dimensional angular momentum-energy distribution of electrons emitted from argon by short laser pulses. We identify characteristic features of both multiphoton and tunneling ionization in the partial-wave distribution for Keldysh parameters close to unity. We observe a remarkable degree of quantum-classical correspondence in the photoinization process which becomes even more pronounced after intensity averaging over the focal volume. We derive an energy-dependent cut-off for the highest angular momentum accessible within the framework of the strong-field approximation, which accurately reproduces the partial wave distributions found from solutions of the time-dependent Schrödinger equation.

We theoretically study time-resolved two-photon double ionization (TPDI) of helium as probed by attosecond streaking. We review recent advances in the understanding of the photoelectric effect in the time domain and discuss the differences between one- and two-photon ionization, as well as one- and two-electron emission. We perform exact ab-initio simulations for attosecond streaking experiments in the sequential TPDI regime and compare the results to the two-electron Eisenbud-Wigner-Smith delay for the process. Our calculations directly show that the timing of the emission process sensitively depends on the energy sharing between the two outgoing electrons. In particular, we identify Fano-like interferences in the relative time delay of the two emitted electrons when the sequential ionization channel occurs via intermediate excited ionic (shake-up) states. Furthermore, we find that the photoemission time delays are only weakly dependent on the relative emission angle of the ejected electrons.

We present an analytical model that characterizes two-photon transitions in the presence of autoionising states. We applied this model to interpret resonant RABITT spectra, and show that, as a harmonic traverses a resonance, the phase of the sideband beating significantly varies with photon energy. This phase variation is generally very different from the π jump observed in previous works, in which the direct path contribution was negligible. We illustrate the possible phase profiles arising in resonant two-photon transitions with an intuitive geometrical representation.

XUV induced dynamics in molecules is still largely unexplored while experimental and theoretical tools are becoming available in several labs. In this work, we present a compact XUV beamline designed to induce and probe femtosecond and attosecond dynamics in gas samples (from atoms to complex molecular species). The induced processes are studied with time-resolved photoelectron or/and photoion imaging. The characterization of the performances of the experimental setup is presented. We show experimental results obtained in naphthalene molecule showing femtosecond and attosecond time-resolved photoelectron imaging experiments allowing electron wavepacket phase measurements.

We investigate from a theoretical perspective time-resolved photoionization of N₂ irradiated by a combination of a long infrared (IR) pulse with a dedicated train of attosecond pulses (APT) in the extreme ultraviolet (XUV) range. The delay time of the attosecond train with respect to the infrared pulse is systematically varied, in accordance with experiments. We find marked oscillations of the ionization yield as a function of delay. We analyze the position of maxima and minima of electron yield and trends with XUV frequency.

Theoretical aspects of photoelectron angular distributions are discussed with reference to bichromatic ionization by an FEL beam. Specifically, we consider an asymmetry in the angular distribution due to interference between the ionization paths from the fundamental and the second harmonic. The case of circularly polarized radiation is analyzed in detail in the vicinity of an intermediate resonance in the two-photon ionization paths. Similarities and differences to interference phenomena due to non-dipole effects are also discussed.

An overview is given of the recently developed adiabatic-nuclei convergent closecoupling method for positron-molecule scattering. Fixed-nuclei single-centre calculations of positron-H₂ scattering are presented. Particular emphasis is given to demonstrating convergence with increasing size of the basis and the projectile partial-wave expansion. Results are converged to within ±5%.

We report on a new attempt at an analysis of the vibrational state distributions in the products of a photo-induced chemical reaction. The experiment was performed by using time- resolved electron momentum spectroscopy (TR-EMS) for the products produced by the three- body photodissociation dynamics of the deuterated acetone molecule at 195 nm. It has been found from a comparison between the experiment and associated theoretical calculations that future TR-EMS measurements with improved statistics could be useful for the vibrational analysis of reaction products, in cases when effects of molecular vibration on their electron momentum densities are large enough so as to be noticeable in the binding energy spectra.

The collision system U⁸⁸⁺ + N₂ at a low-relativistic projectile energy of 90 MeV/u has been analyzed experimentally and theoretically with respect to fast electrons emitted with a velocity v_e close to the projectile velocity, v_p ≈ v_e, at an observation angle of ϑ_e ≈ 0°, i.e., in the direction of the projectile beam. Three distinct processes are identified, where each of the underlying charge-transfer mechanisms leads to a characteristic feature in the asymmetry of the observed electron energy distribution. The experimental results for each of the three processes are compared to the corresponding theoretical models.

The study of chemical reactions between ions and neutral species at very low energies reveals precise informations about the dynamics of collisions and fine details of intermolecular interactions. Here, we report progress towards the development of next- generation experiments for the investigation of cold ion-neutral reactions. First, we present a new ''dynamic" hybrid ion-atom trap which enables the study of collisions with a superior energy resolution accessing a regime in which quantum scattering resonances may become observable. Second, we discuss and numerically characterize the concept and properties of a hybrid trap for cold neutral molecules and molecular ions which paves the way for the study of ion-molecule reactions in the millikelvin regime.

Spin orbit coupling (SOC) for neutral atoms can be synthesized with pulsed or time modulating gradient magnetic field (GMF). This is confirmed through the studies of collective dipole oscillations for a spin-1 atomic condensate in a harmonic trap after abruptly turning on SOC and adiabatically adjusted equilibrium states when SOC strength is slowly ramped up. Further measurements reveal that SOC can be enhanced when the GMF modulation frequency approaches harmonic trap frequency. Additionally, we discuss how the technique of pulsed GMF can be used to synthesize space-period magnetic fields, or magnetic lattices.

We have applied the method of foil-induced Coulomb Explosion Imaging (FCEI) to determine the handedness of a homochiral sample of the compound trans-2,3-dideuterooxirane C₂OH₂D₂. We determined the compound to be of the (R, R)-econfiguration with a statistical significance of 5σ. As the molecular sample was chemically linked to the stereochemical reference standard glyceraldehyde, our assignment constitutes an independent verification of the absolute handedness of all compounds linked to this reference substance.

All molecular forms of life have chemically-specific handedness. However, the origin of these asymmetries is not understood. A possible explanation was suggested by Vester and Ulbricht immediately following the discovery of parity violation in 1957: chiral beta radiation in cosmic rays may have preferentially destroyed one enantiomeric form of various biological precursors. In the experiments reported here, we observed chiral specificity in two electron- molecule interactions: quasi-elastic scattering and dissociative electron attachment. Using low- energy longitudinally spin-polarized (chiral) electrons as substitutes for beta rays, we found that chiral bromocamphor molecules exhibited both a transmission and dissociative electron attachment rate that depended on their handedness for a given direction of incident electron spin. Consequently, these results, especially those with dissociative electron attachment, connect the universal chiral asymmetry of the weak force with a molecular breakup process, thereby demonstrating the viability of the Vester-Ulbricht hypothesis.

In this work we report calculated cross sections for elastic scattering of low-energy electrons by tetrahydropyran (C₅H₁₀O) molecule. We employed the Schwinger multichannel method (SMC) [5] implemented with pseudopotentials (SMCPP) in the static-exchange (SE) approximation for energies up to 30 eV. We compare our calculated cross sections with previous results obtained for cyclohexane and 1,4-dioxane molecules, since their geometrical structures are similar. We found that the differential cross sections obtained in the SE approximation present similar behavior for the three molecules except at lower angles, where the dipole moment present in tetrahydropyran increases abruptly the differential cross sections.

After the laser revolution, a major breakthrough comes from the short wavelength free electron lasers that offer tunable mJ power short pulse light sources for users. Present features and new perspectives will be discussed.

Ultrafast molecular dynamics can be studied using x-rays from both synchrotrons sources and x-ray free electron lasers. Synchrotron studies are limited by the 10-100 ps duration pulses to processes where the Auger lifetime can be used to probe dynamics initiated by excitation of an inner-shell electron to an antibonding orbital. The short pulses produced by x-ray free electron lasers offer the opportunity to study molecular dynamics directly with pump-probe techniques. A two-mirror x-ray split and delay device has been developed for x- ray pump - x-ray probe experiments at the soft x-ray AMO instrument at the LCLS. The device operates over a photon energy range of 250-1800 eV with a variable delay of up to 200 femtoseconds with 0.1 fs resolution.

Fragmentation of complex molecules is studied linking the fragment-ions to the primary vacancies produced in their molecular orbitals. It is observed that a model based in such association describes well rather complex molecules. Deviations from this model are clear indications that inner valence-shells and double ionization plays a key role in the production of some fragments.

The linear polarization of x-rays, emitted from highly-charged ions, has been studied within the framework of the density matrix theory and the multiconfiguration Dirac-Fock method. Emphasis was placed especially on two-photon cascades that proceed via intermediate overlapping resonances. For such two-step cascades, we here explore how the level-splitting of the resonances affects the linear polarization of the x-rays, and whether modifications in the degree of polarization may help determine small level-splittings in multiply- and highly-charged ions, if carefully analyzed along isoelectronic sequences. Detailed calculations are carried out for the 1s2p²J_i = 3/2 → 1s2s2p J = 1/2, 3/2 + γ₁ → 1s²2s J_f = 1/2 + γ₁ + γ₂ radiative cascade of lithium-like W⁷¹⁺ ions. For this cascade, a quite remarkable increase of the (degree of) linear polarization is found for the second-step γ2 photons, if the level-splitting becomes smaller than Δω ≲ 0.2 a.u. ≈ 5.4 eV. Accurate polarization measurements of x-rays may therefore be also utilized in the future to ascertain small level-splittings in multiply- and highly-charged ions.

We have developed a new experimental setup that allowed us to study collision interactions between fast ions and liquid microdroplets under a high vacuum condition. Microdroplets of ethanol are irradiated with 1.0-MeV H⁺ and 2.0-MeV C²⁺ ions. The size distribution of the droplets is evaluated from energy-loss measurements of projectile ions penetrating through the microdroplets. We obtain time-of-flight mass spectra of secondary ions from ethanol droplets. It is demonstrated that coincidence measurements with secondary electrons can distinguish specific ions produced in collisions with the droplets. Production mechanisms of H₃O⁺, C₄H₉O⁺, (C₂H₅)₂OH⁺ in the liquid ethanol are discussed.

Astrophysics is driven by observations, and in the present era there are a wealth of state-of-the-art ground-based and satellite facilities. The astrophysical spectra emerging from these are of exceptional quality and quantity and cover a broad wavelength range. To meaningfully interpret these spectra, astronomers employ highly complex modelling codes to simulate the astrophysical observations. Important input to these codes include atomic data such as excitation rates, photoionization cross sections, oscillator strengths, transition probabilities and energy levels/line wavelengths. Due to the relatively low temperatures associated with many astrophysical plasmas, the accurate determination of electron-impact excitation rates in the low energy region is essential in generating a reliable spectral synthesis. Hence it is these atomic data, and the main computational methods used to evaluate them, which we focus on in this publication. We consider in particular the complicated open d- shell structures of the Fe-peak ions in low ionization stages. While some of these data can be obtained experimentally, they are usually of insufficient accuracy or limited to a small number of transitions.

We investigate the structure and features of an ultralong-range triatomic Rydberg molecule formed by a Rb Rydberg atom and a KRb diatomic molecule. In our numerical description, we perform a realistic treatment of the internal rotational motion of the diatomic molecule, and take into account the Rb(n, l ≥ 3) Rydberg degenerate manifold and the energetically closest neighboring levels with principal quantum numbers n' > n and orbital quantum number l ≤ 2. We focus here on the adiabatic electronic potentials evolving from the Rb(n,l ≥ 3) and Rb(n = 26, l = 2) manifolds. The directional properties of the KRb diatomic molecule within the Rb-KRb triatomic Rydberg molecule are also analyzed in detail.

Electron transfer in collisions between Rydberg atoms and targets that attach free low-energy electrons can lead to the formation of heavy-Rydberg ion-pair states comprising a positive-negative ion pair that orbit each other at large separations weakly bound by their mutual electrostatic attraction. It is shown that measurements of the velocity distribution of the ion-pair states produced in such collisions provide a novel probe of the dynamics of dissociative electron attachment.

We report on a novel correlated electronic decay process following extensive Rydberg atom formation in clusters ionized by intense near-infrared fields. A peak close to the atomic ionization potential is found in the electron kinetic energy spectrum. This new contribution is attributed to an energy transfer between two electrons, where one electron decays from a Rydberg state to the ground state and transfers its excess energy to a weakly bound cluster electron in the environment that can escape from the cluster. The process is a result of nanoplasma formation and is therefore expected to be important, whenever intense laser pulses interact with nanometer-sized particles.

The identification of sources for applications that include nanolithography, surface patterning and high resolution imaging is the focus of a considerable activity in the extreme ultraviolet (EUV) or soft x-ray (SXR) spectral regions. We report on the result of a study of the spectra from laser produced plasmas of a number of medium and high Z metals undertaken in order to identify potential sources for use with available multilayer mirrors. The main focus was the study of unresolved transition arrays emitted from ions with 3d, 4d and 4f valence subshells that emit strongly in the water window (2.34-4.38 nm).and that could be used for biological imaging or cell tomography.

Charge state and energy loss measurements of slow highly charged ions (HCIs) after transmission through nanometer and sub-nanometer thin membranes are presented. Direct transmission measurements through carbon nano membranes (CNMs) show an unexpected bimodal exit charge state distribution, accompanied by charge exchange dependent energy loss. The energy loss of ions in CNMs with large charge loss shows a quadratic dependency on the incident charge state, indicating charge state dependent stopping force values. Another access to the exit charge state distribution is given by irradiating stacks of CNMs and investigating each layer of the stack with high resolution imaging techniques like transmission electron microscopy (TEM) and helium ion microscopy (HIM) independently. The observation of pores created in all of the layers confirms the assumption derived from the transmission measurements that the two separated charge state distributions reflect two different impact parameter regimes, i.e. close collision with large charge exchange and distant collisions with weak ion-target interaction.

In a recent experiment we demonstrated the possibility to suppress the thermal hysteresis of the phase transition in giant magnetocaloric MnAs thin film by interaction with slow highly charged ions (Ne⁹⁺ at 90 keV) [1]. This phenomenon has a major impact for possible applications in magnetic refrigeration and thus its reproducibility and robustness are of prime importance. Here we present some new investigations about the origin and the nature of the irradiation-induced defects responsible for the thermal hysteresis suppression. Considering in particular two samples that receive different ion fluences (two order of magnitude of difference), we investigate the reliability of this process. The stability of the irradiation-induced defects with respect to a soft annealing is studied by X-ray diffraction and magnetometry measurements, which provide some new insights on the mechanisms involved.

We have studied diffractive scattering of H₂ from LiF(100) under fast grazing incidence, as a function of the initial ro-vibrational state of the molecule. We show that diffraction patterns, i.e., the relative diffraction peaks intensity, vary significantly with the initial ro-vibrational state. This result indicates that in order to perform accurate comparisons between experimental and theoretical results, some knowledge about the initial ro-vibrational distribution of the molecular experimental beam is required. We hope that this result will encourage experimental groups working on the field to design and develop the techniques required to provide such information.

Absolute total cross sections for electron scattering from He, Ne, Ar, Kr and Xe at very low electron energies are presented. The cross sections were obtained using the threshold- photoelectron source, which employs a combination of the penetrating field technique together with the threshold photoionization of atoms by synchrotron radiation. Obtained total cross sections for electron scattering from these noble gas atoms generally agree well with those obtained in the previous experiments above 100 meV, where several experimental works have been reported. Comparison of the measured cross section for He with that of theoretical ones shows very good agreement at very low energies even below 10 meV, which confirms the validity of theoretical cross sections of He which have been regarded as the 'standard' cross sections. Scattering lengths for the e^- - noble gas scatterings determined from the our cross sections using the modified effective range theory (MERT) showed that scattering lengths for He and Ne agree well with the values obtained in the previous experimental and theoretical studies. On the other hand, in case of heavier noble gas atoms, significant discrepancies were found between the scattering lengths derived from MERT analysis to our total cross sections and those reported in previous studies.

Triply differential cross sections for the electron induced ionization of the 3a₁ and 1b₁ orbitals of the water molecule are calculated within the distorted wave Born approximation. The distorted wave functions are numerically calculated by modelling both the initial and the final channels whereas single-center Slater type wave functions are used for describing the molecular target. A good agreement with the existing experimental data is obtained.

We present an overview on the photoactivation of gaseous peptide ions and point out the importance of synchrotron-based activation of peptides and proteins. Particularly, we present results on the action spectroscopy of substance P peptide in vacuum-ultraviolet (VUV) and discuss the importance of VUV -induced neutral losses over a wide photon energy range.

Multiple ionization of ions subsequent to absorption of a single photon has been studied employing a photon-ion merged-beam setup at the PETRA III synchrotron radiation facility of DESY in Hamburg. Absolute cross sections for single, double and triple ionization of C⁺ ions were measured with emphasis on specific well defined terms of K-shell excited C⁺. In particular, the terms C⁺ (1s2s²2p^{2 2}D,²P) were excited from the ground level of C⁺. Subsequent autoionization processes resulted in the production of C²⁺, C³⁺ and C⁴⁺ ions. The associated decay mechanisms are single-Auger, double-Auger and triple-Auger decay. The observation of C⁴⁺ products arising from C⁺(1s2s²2p^{2 2}D,²P) unambiguously confirmed the existence of triple-Auger decay, i.e., a process in which 4 electrons interact with one another such that one fills the K-shell vacancy and the others are simultaneously ejected. The experiment yields branching ratios for the Auger decay channels as well as individual decay rates for autoionization and radiative stabilization of the C⁺(1s2s²2p^{2 2}D,²P) terms.

In this article we report new results for action spectroscopy of protonated peptide Leucine enkephalin (YGGFL). By coupling a linear ion trap mass spectrometer with a vacuum ultraviolet (VUV) synchrotron radiation beamline, we investigate photofragmentation pattern of this peptide, through the analysis of tandem mass spectra recorded over a range of VUV photon energies, below and above the ionization energy. The obtained fragmentation patterns are discussed and compared to previous results.

A series of ion storage experiments on small carbon cluster anions was conducted to understand size-dependent cooling processes. The laser-induced delayed electron detachment time profile show clear even/odd alternation due to the presence of the electronic cooling. The time evolution of the internal energy distribution was simulated for C_n^- (n=4 to 7) with a common procedure taking vibrational and electronic cooling into account.

Non-statistical fragmentation processes are important when Polycyclic Aromatic Hydrocarbon (PAH) molecules, fullerenes, or other large molecules collide with atoms at center- of-mass energies from a few tens to a few hundreds of eV. The typical result is the prompt, billiard-ball-like knockout of single atoms (CH_x-loss). This is distinct from the well-known statistical fragmentation patterns of these molecules, which are dominated by H- and C₂H₂-loss for PAHs and C₂-loss for fullerenes. We have explored the role of non-statistical fragmentation of PAHs and fullerenes in a series of experimental and theoretical studies. In general, the yield of non-statistical fragments depends sensitively on their stability against secondary statistical fragmentation following knockout.