Table of contents

This article has been retracted as it was published in error.

Retraction published: 22 September 2015

We measure isotope effect in strong-field ionization and dissociation of molecular hydrogen using a mixed-gas target in a Reaction Microscope (REMI). We compare experimental results with theoretical predictions.

Using VUV radiation several ionic fragments were observed from the multiphoton dissociation of the Nitromethane. The detection of the molecular ions was focused on: HCO⁺, NO⁺, CNOH⁺ and CH₃⁺ due to their importance in reactions involving the formation of molecules in the interstellar clouds and the surrounding regions of the stars.

The spatial distribution of electric charges forming a square well potential has been analyzed. It has been shown that two concentric spheres each with a double layer of charges create the potentials of this type. It has been demonstrated that the phenomenological potentials simulating the potential of C₆₀ shell belong to a family of potentials with non-flat bottoms. A C₆₀ shell potential has been calculated under the assumption that it is formed by the averaged charge density of a neutral atom. It has been shown that this potential has a cuspshaped form. Two model potentials of that type are proposed and their parameters have been calculated.

Dissociation and ionization of formic acid was investigated by multiphotonic absorption regime using laser pulse at 355nm in conjunction with TOF mass spectrometry in reflectron mode (R-TOF). From the different type of detected fragment ions is inferred the formation of some small clusters of formic acid.

An electronic structure of the negative ion C₆₀^2- has been studied. It is found that in the first approximation of the variational method (when a trial wave function of the extra electrons is a product of one-electron functions) the total energy of the system is negative and that the second electron affinity (EA) of the C₆₀ molecule within the utilized model potentials is about 1 eV. The photodetachment cross sections of the C₆₀^2- ion have been calculated as well; they are found to exhibit two different threshold behaviors with their values being of the same order as the photodetachment cross sections of atomic negative ions with the same EA.

Modelling of the C₆₀ cage by a square-well potential U_c(r) is a popular approximation. In the literature, some inconsistency is present in choosing the magnitudes of parameters of U_c(r). In the present study, e + C₆₀ and e + A@C₆₀ elastic scattering is scrutinized versus the parameters of U_c(r) in order to identify U_c(r) which is best suited for studying electron-fullerene scattering and how the latter can be controlled by tuning the potential.

The study focuses on rapid nuclear rearrangement/isomerization taking place in an early stage of butadiene fragmentation using multiple ion momentum imaging spectroscopy and tunable synchrotron radiation. In addition, ab initio calculations are performed to disentangle the nuclear dynamics preceding dissociation.

The ultrafast dynamics of pure and doped helium nanodroplets is studied using VIS and XUV femto-second pump-probe spectroscopy in combination with ion and electron imaging detection.

We measured and calculated the PECD of three different halogenated chiral molecules in order to study the role of the localization of the initial orbital of the outgoing electron with respect to the chiral center.

We present an experimental and theoretical study of resonant inelastic x-ray scattering (RIXS) in the CS₂ molecule near the S 1s edge. We show that localization of the S 1s core-hole occurs in CS₂ during the RIXS process due to the orientational dephasing of interference between the waves scattering on the two sulfur atoms. Strong evolution of the RIXS profile with the excitation energy far below the first absorption resonance reflects the onset of electron dynamics triggered by a coherent excitation of multiple electronic states.

The results of calculated vibrational predissociation (VPD) of water dimers are presented. The VPD processes considered here are the followings: initially closed channel of symmetric stretching mode is excited by one quantum, and dissociate to two open channels of the bending mode excitation by one quantum in the donor and acceptor units. The VPD rate constants are calculated in the quantum mechanical approach under the adiabatic approximation. The channel interactions were taken into account in and between the initial and final states. The results obtained by quantum-mechanical approach are compared with both experimental and semi-classical trajectory calculation results.

Molecular orbitals for the water molecule obtained from a potential model are represented on a three- dimensional Cartesian mesh. The Schrödinger equation describing the molecule exposed to a strong DC electric field is solved to obtain the resonance parameters (position and line width, i.e., lifetime) as a function of field orientation and for field strengths for which the outer classical turning point is within the computational grid.

Action spectroscopy provides key insights into the nature of electronic transitions of coordination complexes such as porhyrin-containing biochromophores like chlorophyll or transition metal complexes such as tris(bipyridine)ruthenium.

The angular correlation functions of a pair of Lyman-α photons in the photodissociation of H₂ are measured more precisely than in the early experiments [Nakanishi et. al., Phys. Rev. A.90, 043405(2014)]. The linearly polarized light is used to excite the photodissociation via the doubly excited Q₂¹Π_u(1) state.

In this contribution we will discuss the field free laser induced spatial alignment of hexapole quantum state selected methyl iodide. We will demonstrate that we have control over the spatial alignment and can chose P₂(cos θ) between 0.7 and -0.1 coupled to P₄(cos θ) between 0.3 and 0.0. The effect of the relative orientation between a static electric field and a strong laser field on the structure of the field free rotational alignment revivals will be discussed.

We report experimental results on strong-field laser interact with aligned CH₃CI molecules, the ejection of fragments H_n⁺ dependent on alignment of CH₃Cl molecules has been studied. The mechanism of fragmentation builds on the alignment sensitive ionization and dissociation from inner and outer valence orbitals or the excitation process of molecular have been discussed.

We have measured the Recoil Frame - Photoelectron Angular Distributions (RF-PADs) for inner-shell photoionization of CH₃F, CH₃I and CF₃I halomethane molecules for photoelectron energies up to 300 eV detected within a 4π solid angle in the gas-phase. For high kinetic energies, the RF-PADs are dominated by diffraction effects that encode information on the molecular geometry.

The ionization of the hydrogen molecular ion H₂⁺ by twisted Bessel light has been theoretically investigated. Special attention is paid to scenario where the twisted radiation interacts with a macroscopic target which consists of randomly distributed but aligned H₂⁺ molecules. We demonstrate for this case that the angle-differential photoionization cross section is sensitive to the transverse momentum of the incident light and alignment angle of molecules.

A new method for a complete theoretical description of Interatomic Coulombic decay (ICD) in large polyatomic rare-gas clusters will be presented. This original method combines the projection-operator formalism of resonant scattering theory, the diatomics-in-molecules technique and a surface hopping algorithm. Such combined approach has fairly low computational costs and constitutes an efficient tool for studying ICD in polyatomic clusters. Benchmark examples will be given to illustrate the method. Results on ICD in large rare-gas clusters will finally be reported.

We predict resonant hybridization of Auger and intercoulombic decay (ICD) processes in the photoionization of Kr@C₆₀ using the time-dependent local density approximation (TDLDA) for the calculation.

Creation of deep core holes leads to extensive nuclear dynamics on a few femtosecond timescale despite the very short (τ ≤ 1 fs) lifetime of such states. This is because the 1^st steps of the relaxation processes (i.e. both radiative and non-radiative decays) generate intermediate states with one and multiple holes in core orbitals. As an example, ultrafast dissociation is observed in three well-distinguishable LVV Auger decay channels for HCl following Cl1s→σ^* excitation.

We investigate effects of electron correlations on the attosecond time delay of the photoionization from HOMO and HOMO-1 electrons in C₂₄₀. A comparison with earlier C₆₀ results assesses the molecular size effect.

Near sulfur K edge photoionization of the SF₆, molecule has been studied for X-ray photons. Total and partial photoion yields for the fragmentation products have been recorded as a function of the incident photon energy. The atomic fluorine ion, F⁺, dominates the mass spectra in the energy range studied in this paper. The intensity of absorption for the dipole-forbidden but vibronically allowed transition S K (1a_1g→6a_1g) was calculated for the first time. This transition is shown to play a part in the fragmentation profile.

Dissociative ionization of NO, NO → NO⁺ + e⁻ → N⁺ + O + e⁻, in ω-2ω two-color phase-controlled intense laser fields was investigated by three-dimensional ion momentum imaging. The momentum image of the N⁺ ion exhibited anisotropic distributions peaked at 35° against the laser polarization, which show clear left-right asymmetry depending on the ω-2ω relative phase. The present study demonstrates that the molecular orbital can be retrieved by distinguishing the difference between the N and O side from the fragment anisotropy by intense laser pulses.

A new method is proposed to perform Quantum Wave Packet Nuclear Dynamics on large systems, by making use of information obtained by Semi-Classical Quantum Dynamics. The key of the method resides in expressing the nuclear wave function of the system in a basis set determined by the positions of multiple trajectories at each time.

We have measured angle-resolved rescattering photoelectron spectra induced by ultrashort intense near-IR laser pulses at 1200-1650 nm. From the spectra, we have extracted field-free electron-ion differential scattering cross sections and compared them with theoretical calculations.

We present results of VUV action spectroscopy of gas-phase protonated Leucin-Enkephalin peptide. The experiment has been performed by coupling a linear quadrupole ion trap with a synchrotron radiation VUV beamline.

We report on experimental and theoretical study of collective Auger decay of double inner-valence vacancy in fluoromethane, in which two electrons simultaneously fill the vacancies and a third electron is ejected to continuum. Calculations predict the respective lifetime of the double vacancy state to be in the femtosecond range, typical for two-electron Auger decay. Measured electron spectra indirectly support this rather surprising result.

Direct, time-domain measurements are reported for the lifetimes of the lower-lying vibrational levels of the 3p_z Rydberg state of the methyl radical. Lifetimes measured are in the region of hundreds of femtoseconds, and show a decrease with increasing vibrational activity. The mechanism is interpreted with the aid of ab initio calculations.

We show that the interplay of electron removal and nuclear dynamics on the few femtosecond range, controlled by the duration of few-cycle laser pulses, determines the ratio of C₂H₄³⁺ fragmentation into two respectively three moieties.

Using a double-pulse scheme we visualize and control molecular dynamics taking place on intermediate states populated during different sequential double ionization pathways of CO₂. Exchanging the pulse- sequence can almost completely switch the pathway.

Photo-absorption from short and intense Xray pulses by a molecule or a cluster triggers a complicated electron and ion dynamics. Whereas the excitation process concerns largely core-shell electrons, there are various subsequent relaxation channels like electronic decays and ionic Coulomb explosion. We will discuss the interplay of those processes for molecular clusters and fullerenes.

Resonance-enhanced multiphoton ionization of H₂⁺ exposed to elliptically polarized VUV laser pulses is investigated. Differential cross sections for nuclei and electron are obtained using numerical solutions of the time-dependent Schrödinger equation. In this work in progress, we explore the dependence of the dissociative ionization observables with the polarization of the light.

The cooled molecular beams of acenes compounds as naphthalene C₁₀H₈, anthracene C₁₄H₁₀, and ben- zantracene C₁₈H₁₂, were produced by adiabatic expansion in high vacuum chamber, 10^-8 torr. Molecular beams interacted with laser radiation of 266 and 355 nm, from a Ng:YAG laser at intensities up to 10¹⁰ W·cm^-2 At higher intensities the multiple photon absorption was possible. The number of photons was calculated using Keldysh approach. The dominant photophysics of photon-molecule interactions were photodissociation and photoionization processes depending on the wavelength used during the experiment.

Two identical XUV attosecond pulses interact with the hydrogen molecule creating an interferometer resulting from the direct and sequential two-photon absorption paths reaching the same final ionized states. The dependence of the ionization yields with the time delay between the pulses allows to reconstruct the pumped vibronic (electronic and vibrational) wave packet created in the singly excited states of the molecule. The use of XUV pulses avoids a laser-induced distortion of the molecular potential, ensuring the characterization of the intrinsic behaviour of the system.

We use a UV-pump/IR-probe scheme, combining a single attosecond UV pulse and a 750 nm IR pulse, to explore laser-assisted photoionization of the hydrogen molecule in the autoionization region. The electron energy distributions exhibit unusual streaking patterns that are explored for different angles of the electron ejection with respect to the polarization vector and the molecular axis. Moreover, by controlling the time delay between the pulses, we observe that one can suppress the autoionization channel.

The fragmentation of 2Br-, 2Cl- and 5Br-pyrimidine following direct valence photoionization or inner shell excitation and decay has been studied by electron-ion coincidence experiments. The results show that the fragmentation is strongly selective on the final singly charged ion state and the dominant fragmentation patterns correlate to the nearest appearance potential.

We are developing an ab initio numerical method to compute molecular single and double ionization processes induced by intense laser pulses. We present our first time-dependent simulations in the H₂⁺ molecular ion including both electronic and nuclear degrees of freedom. We compare different methods for the extraction of excitation and ionization probabilities from the numerical time-dependent wave function, which will be applied to more complex targets in the future.

We demonstrate the importance of ionization from Rydberg orbitals via experimental and theoretical work focusing on the strong-field dissociative single ionization of small hydrocarbons. Our findings suggest that Rydberg states should be routinely considered when studying polyatomic molecules in intense laser fields.

We focus on the dissociation of metastable molecular dications induced by intense, ultrafast laser pulses. In particular, we demonstrate the dominant role of commonly-neglected permanent-dipole transitions and drive dissociation via a pump-dump-like mechanism within a single laser pulse.

We demonstrate control over fragmentation of H₂⁺ and D₂ molecules via the carrier-envelope phase of sub-5 fs laser pulses. Moreover, we attribute our findings to interferences between different pathways involving different net numbers of photons, revealing "high-order" pathways and the importance of the bandwidth.

A new approach to the half-scattering problem is introduced and demonstrated on several of the challenging applications in laser-matter interaction: precision single photo-electron spectra, fully differential doubleemission spectra at near IR wave-length, and emission from multi-electron systems. A long-standing discrepancy between theory and measurement in the orientation dependence of CO₂ ionization is resolved. Application to many-body systems will be demonstrated and extension to the full scattering problem will be discussed.

The multicenter nature of molecules can affect the strong field ionization. By studying the resonancelike enhancement structure in the high-order ATI spectrum of C₂H₄ and C₂H₆, we illustrate how the multicenter effect contributes to the molecular tunneling ionization. We find the hydrogen contributions lead to the weak resonance-like structure of C₂H₆ but have no affect for C₂H₄, this target dependence origins from their different HOMO structures. Those conclusions are supported by Strong Field Approximation calculation.

The vibrationally resolved C 2s photoionization cross-section of methane was investigated both theoretically and experimentally. When compared to that of C 1s photoionization, a rather different pattern has been observed, suggesting a strong interplay between the electron diffraction and interference effects.

Photodissociation of the pyridine molecules has been studied experimentally over the 16-70 eV photon energy range. Formation of the excited NH(A³Π) radicals has been observed among several other atomic and dia-tomic fragments, using the photon-induced fluorescence spectroscopy. Since the pyridine molecules do not con-tain the NH structural units, this is an indication of the bond rearrangement processes associated with migration of the hydrogen atoms prior to dissociation. The plausible mechanisms for the NH formation will be discussed.

We investigated the fragmentation of glycine molecule induced by resonant Auger-decay following core-shell ionization at different atomic sites by synchrotron light. We show that the dissociation pathways as well as the charge state distributions are modified due to core-level photoionization followed by Auger-decay at the different target atomic sites. The initial states for the dissociation are associated with vacancies in valence or inner-valence shells that are not localized as in core shells. We also compare the molecular dissociation following resonant and non-resonant Auger decay processes to gain insight into the influence on bond cleavage by different ionization mechanisms.

By analyzing the photodissociation process of the D⁺₂ molecule, we found a robust effect in the angular distribution of the photofragments which serves as a direct signature of the light-induced conical intersection (LICI) providing undoubted evidence for its existence.

We report on new data regarding on the photoionization and fragmentation dynamics of gas phase endohedral fullerenes Ho₃N@C₈₀ obtained with intense femtosecond X-ray pulses from the Linac Coherent Light Source (LCLS) free electron laser (FEL).

We present the first-ever measurement of nondipole chiral angular distribution parameters for C 1s photoemission from each enantiomer of camphor in the photon energy range 296-343eV using linearly polarized light. The angular distribution parameters are determined to be enantiomer-specific, suggesting a new form of linear dichroism.

The cryogenic trap for fast ion beams (CTF) located at the Max-Planck-Institut für Kernphysik has been used to study laser-induced delayed electron emission of various molecular and metal-cluster anions. We will discuss recent experiments investigating the radiative cooling respectively heating of Co⁻₄ anions produced in hot and cold ion sources. The experiments will be continued at the cryogenic storage ring (CSR), which is presently being commissioned, to disentangle laser-induced electron emission from atom or cluster dissociation.

We have developed a new setup to measure temperature dependence on vacuum ultraviolet absolute photoabsorption cross sections for linear triatomic molecules from room temperature (∼300 K) up to 700 K. The setup consists of a stainless steel absorption-cell wrapped by sheath wires of 1.2φ in diameter and 2 m length. For the first set of measurement on CO₂ in the photon energy range 10.6 – 11.8 eV, we found that the cross section values at room temperature are in very good agreement with previous measurements as well as the temperature dependence on the cross sections are clearly observed in the measured temperature range.

We report on photoionization studies of Xe.CF₄ and Kr.CF₄ van-der-Waals (vdW) clusters produced in a supersonic expansion and detected using synchrotron radiation and photoelectron- photoion coincidence techniques. Complementary ab initio calculations of the potential energy surfaces for the ground state and the first ionized state are performed and show generally good agreement with the experimental results. In particular, the calculation reveals a change in the equilibrium configuration from face to vertex geometry upon ionization. This observation is fully in line with the lineshapes of the Xe.CF₄ and Kr.CF₄ clusters in the photoelectron spectra.

In recent years double core-hole states are intensively studied since their chemical shifts provide detailed information about initial-state and relaxation effects in a molecule. We derived the Si 1s⁻¹, 2s⁻¹, and 2p⁻¹ binding energies as well as the Si 2s⁻², 2s⁻¹, 2p⁻¹, and 2p⁻² double-core hole binding energies of different SiX₄ systems in order to derive the chemical shifts. Based on these results we created Wagner plots, which give insight in the initial state and the relaxation effects in the different molecules.

Soft X-ray absorption spectra of the lowest excited triplet states of several organic molecules (quinones, benzaldehydes, and other carbonyls) and potential curves of valence- and core- doubly excited states are calculated for the O 1s region.

Collective excitation in polycyclic aromatic hydrocarbon molecule is studied in collision experiments with intermediate velocity (50-180 keV) proton and FUV (15-40 eV) photon energy. In proton impact experiments a clear comparison between pure ionization and capture ionization (or pure capture) process is done on the basis of ionization, evaporation, fragmentation process as a function of impact energy. Two mechanisms: large impact parameter collective excitation mode and closer encounters with higher amount of electronic energy loss leading to fragmentation were observed in proton collision process. The photon impact results were used to understand the origin of evaporation processes.

Upon ionization of ground state O₂ molecules in a short XUV pulse, we observe a time-dependent vibrational wave packet in the potential of the binding O⁺₂ (a⁴Π_u) state. Our pump–probe delay dependent kinetic-energy-release (KER) spectra are in qualitative agreement with the results of coupled-channel simulations that are based on calculated Born-Oppenheimer potential-energy curves (PECs). Using a Morse potential adjusted to the experimental data most features of the experimental spectra are reproduced quantitatively.

A network of ion sources is being developed on the 300-kV acceleration platform of the cryogenic storage ring (CSR) at the Max-Planck-Institut für Kernphysik. It consists of several types of sources like a metal ion sputtering source (MISS), a Penning source, a laser vaporization (LVAP) source, and an electrospray ionization (ESI) source to produce a large variety of ions which can be studied for photon and electron interaction in a ro-vibrationally cold environment. Furthermore a storage device such as a radiofrequency quadrupole (RFQ) is foreseen for internal state cooling and accumulation of rarely produced species.

The time resolved photoionization of C 1s in uracil following excitation of the neutral molecule by 260 nm pulses has been studied at LCLS.

Double-slit experiments illustrate proof for wave–particle complementarity. The essence of Einstein–Bohr's debate about wave–particle duality was whether the momentum transfer between a particle and a recoiling slit could mark the path, thus destroying the interference. We realized this recoiling double-slit gedanken experiment by resonant X-ray photoemission from molecular oxygen for geometries near equilibrium (coupled slits) and in a dissociative state far away from equilibrium (decoupled slits). Interference is observed in the former case, while the electron momentum transfer quenches the interference in the latter case.

An experimental and theoretical investigation of the VUV photofragmentation of CH₂I₂ molecule is reported. The work focuses on the I-loss channel. The experimental results demonstrate that at energies lower than 12 eV diiodomethane radical cation dissociates only into the CH₂I⁺ ion and an I atom while the theoretical calculationsshow that isomerisation of [CH₂I₂]⁺ into iso-diiodomethane [CH₂I-I]⁺ intermediates can occur before the loss ofiodine atom.

In this work, we show that the direct determination of a chiral molecule's absolute configuration can be achieved with Coulomb Explosion Imaging in a COLTRIMS reaction microscope. We compare the results after ionisation with femto-second laser pulses and with X-ray synchrotron light. Different fragmentation pathways of the prototypical chiral molecule CHBrClF are identified that carry information on the handedness. The applicabilty of the technique towards bigger molecules is discussed.

We report on the dynamics of photoexcitation and photoionization induced by ultrashort strong optical pulses in two medium sized polyatomic molecules, 1-azabicyclo[2,2,2]octane and caffeine. The time-dependent Schrödinger equation is solved for an electronic Hamiltonian that includes the interaction with the strong pulse. The partitioning technique is applied to include both the neutral and the ionized subspaces.

We present a comprehensive analysis of autoionization processes in Ne clusters (~5000 atoms) after multiple valence excitations by free electron laser radiation. The evolution from 2-body interatomic Coulombic decay (ICD) to 3-body ICD is demonstrated when changing from surface to bulk Frenkel exciton excitation. Super Coster-Kronig type 2-body ICD is observed at Wannier exciton which quenches the main ICD channel.

We report on a theoretical investigation on ultrafast dynamics induced in the neutral and cationic states of the PENNA molecule by a short, strong optical pulse. The ultrafast, short time, electronic dynamics is computed by solving the time-dependent Schroedinger equation for the time-dependent Hamiltonian that includes the coupling to the strong field. The partitioning technique is implemented to take into account the coupling to the ionization continua. Preliminary results on the onset of nuclear dynamics that follows the excitation by the pump pulse will be discussed.

We report experimental observation of "slow" fragmentation from ethylene molecules on nanosecond or even microsecond timescale after their interaction with femtosecond laser pulses. Our results indicate that such fragmentation process originates from meta-stable high-lying vibrational states of ethylene ions.

We extend attosecond transient absorption spectroscopy (ATAS) to the study of hydrogen molecules, demonstrating the potential of the technique to resolve – simultaneously and with state resolution – both the electronic and nuclear dynamics.

We perform an experimental investigation on tunneling ionization of CH₃X (X=I, Br, Cl) molecules in intense femtosecond laser fields (10¹³ to 10¹⁵ W/cm²). The angular distribution of the parent and fragment ions from the well aligned molecular targets has been measured. Compared with theoretical calculation, the results show some new insights into the ionization mechanism of these molecules in intense laser fields.

C⁺₆₀ has been proposed to be responsible for two of the diffuse interstellar bands (DIBs), the absorption features observed in the visible-to-near-infrared spectra of the interstellar medium. However, a confirmation requires laboratory gas-phase spectra, which are so far not available. We plan to develop a novel spectroscopy technique that will allow us to obtain the first gas-phase spectra of C⁺₆₀, and that will be applicable to other complex organic molecules such as polycyclic aromatic hydrocarbons. The current status of the experimental setup, the ideas behind the measurement scheme and the preparatory work toward its implementation will be presented.

We explore the implementation of generalized Sturmian functions for the study of ionization of molecules by photon or electron impact. A first part is devoted to finding a good enough description of the molecular model scattering potential and imposing accurate asymptotic boundary conditions to the molecular continuum wave functions. A second part deals with the calculation, within a generalized Sturmian approach, of single ionization cross sections for small molecules such as CH₄, H₂O and NH₃. Issues related to the random molecular orientation are addressed.

We perform time-dependent local density functional calculations of the time delay in C₆₀ HOMO and HOMO-1 photoionization at giant plasmon energies. A semiclassical model is used to develop further insights.

In this work we explore the high-order harmonic generation in the H₂⁺ molecule under the action of phase shaped pulses. To this end, quantum mechanical wavepacket calculations are performed within a collinear model of H₂⁺. We analyze the effect of a chirp to the plateau extension of the HHG spectrum, observing significant differences with respect to the sign of the chirp parameter. This result is found to originate from a subtle electron recollision dynamics within the chirped laser pulses, as substantiated by classsical trajectory calculations. Extension of this work focuses on including the nuclear motion of H₂⁺.

We present experimental results for AEPICO measurements following core photoionization of N2 molecules, with using an AEPICO spectrometer in which a toroidal electron energy analyzer and an ion momentum spectrometer are installed.

The relaxation dynamics of an ionized/excited molecular system leads to different fundamental processes occurring at sub-femtosecond timescales. Time-resolved XUV-pump XUV-probe experiments should allow deeper insight to the key roles of these processes. Such studies should be feasible soon thanks to experimental schemes similar to those at the high-intensity high-order harmonic generation beamline at the Lund Laser Centre.

An ultrashort XUV laser pulse ionizes the D₂ molecule creating an electronic and nuclear wave packet, with the dominant contributions from the 2sσ_g and 2pπ_u ionic states. A delayed interaction with a 780 nm IR field ejects the second electron, leading to the Coulomb explosion of the molecule, whose nuclear fragments, recorded in coincidence, map the dynamics associated to those two ionic excited states. By varying the orientation of the light polarization, one can control the molecular dynamics by modifying the ratio between the ionic states. Experimental and ab initio theoretical data are jointly reported.

The electronic properties of vanillin molecule were investigated by different excitation and ionization techniques. The Ionic fragmentation mechanisms were studied using time-of-flight mass spectrometry as a function of the energy of the incident radiation in the valence energy region and the inner and core levels. It was stablished as a general feature that the ruptures related to the oxygen atoms are predominant at all energies. The resonances and ionization potential of the oxygen 1s was also determined by NEXAFS spectra.

Using intense photon beams from the XFEL free electron laser, the COLTRIMS Reaction Microscope will be a versatile tool for examination of the dynamics in small quantum systems.

For gas-phase experiments on complex biomolecular ions, the target density is a most critical issue.

We developed a novel high-current electrospray ionization source, delivering 10 times higher currents than conventional systems.

We present a time-dependent many-body theory that is based on the propagation of the two-particle reduced density matrix (2-RDM) [1]. We apply our method to simulate the non-linear response of one-dimensional lithium hydride in femtosecond mid-IR laser pulses.

The effects of entanglement on the spontaneous decay of a pair of H(2p) previously observed by Tanabe et al. (Phys. Rev. A82, 040101 (2010)) could not be reproduced despite careful determination of emission times with respect to the synchrotron bunch.

We discuss the implementation (https://commons.lbl.gov/display/csd/LBNL-AMO-MCTDHF) of Multiconfiguration Time-Dependent Hartree-Fock for polyatomic molecules using a Cartesian product grid of sinc basis functions, and present absorption cross sections and other results calculated with it.

We present a method by which the internuclear distance-dependent decay width ᴦ(r) of Interatomic Coulombic Decay can be obtained using a measured energy distributions and a classical nuclear dynamics model.

In this work we study the effect of fullerene confinement on the triple differential cross section (TDCS) for double ionization of atoms. We compare the results corresponding to the free case with single cage C₆₀ and two cage C₆₀@C₂₄₀ confinement.

We present the first step of a general study on induced damage by ¹²⁵I in water at the molecular level.Requirements for such a study are introduced and preliminary results on the emission spectra of ¹²⁵I seeds are presented.

We analyzed electron production by noble metal nanoparticles irradiated by photons and fast ions. For that, photoabsorption spectra of several gold clusters were calculated in a broad photon energy range by means of time-dependent density-functional theory (TDDFT). Two dominant peaks appearing in the spectra of electron emission of noble metal clusters were assigned to two distinct types of collective electron excitations. This study revealed that the decay of the collective excitations formed in the nanoparticles is an important mechanism of generation of low-energy electrons, which are known to act as important agents of biodamage.

In order to have access to fine phenomena such as ultrafast nuclear dynamics and electronic state - lifetime interferences (ELI) at high energies (few keV), one has to rely on great experimental resolution. The new experimental HAXPES endstation at the GALAXIES beamline of the French synchrotron SOLEIL provides photons in the 2-12 keV energy range along with a total instrumental resolution below 500 meV. In this work we show experimental evidences of ultrafast nuclear dynamics and ELI on HCl and CH₃Cl excited around the Cl 1s resonance. We show also simulations that allow to disentangle the contribution of nuclear dynamics and ELI in our experimental spectra.

The simultaneous core ionization and core excitation process (or K^-2V process) induced by absorption of a single photon provides the basis of a new spectroscopy that offers both advantages of X-ray Photoelectron Spectroscopy (XPS) and near-edge x-ray absorption fine structures (NEXAFS) spectroscopy

The molecular fragmentation of doubly charged L-alanine in gas phase was studied in radiation synchrotron experiments. In this presentation, we summarize our theoretical study on the dynamics of this fragmentation, using various computational methods. We show that in practice the ground state MD simulations are able to statistically reproduce the experimental results of the photo-fragmentation initiated at the excited state.

Due to electronic many-body effects, the ionization of a molecule can trigger ultrafast electron dynamics appearing as a migration of the created hole charge throughout the system. Here we propose a scheme for control of the charge migration dynamics with a single ultrashort laser pulse. We demonstrate by fully ab initio calculations on a molecule containing a chromophore and an amine moieties that simple pulses can be used for stopping the charge-migration oscillations and localizing the charge on the desired site of the system. We argue that this control may be used to predetermine the follow-up nuclear rearrangement and thus the molecular reactivity.

We report experimental observation of the long predicted but experimentally elusive Efimov state of ⁴He trimer by means of Coulomb explosion imaging. We show spatial images of an Efimov state, confirming the predicted size and a typical structure where two atoms are close to each other while the third is far away.

Calculations of the potential energy curves of diatomic molecules are performed for the entire range of internuclear separation in order to correlate Rydberg orbitals at the united atom and separated atoms which are needed to properly assign highly excited Rydberg states.

We present a theoretical study of the vibrationally resolved core photoionization of the water molecule up to high photon energies. In order to understand the role of the coupled electron-nuclear motion in polyatomic molecules, we thus have implemented a new methodology to describe all vibrational modes of a polyatomic molecule. We show our preliminary results on the O(1s) photoionization, with special focus on the vibrationally resolved cross sections in a large range of photon energies, reaching up to 1500 eV.

Here we demonstrate the smallest possible implementation of an antenna-receiver complex which consists of a single (helium) atom acting as the antenna and a second (neon) atom acting as a receiver.

Interatomic Coulombic Decay in mixed NeKr dimers has been measured time-resolved and the nuclear dynamics of the decay have been investigated.

We wish to understand the processes underlying the ionization dynamics of N₂ as experimentally induced and studied by recording the kinetic energy release (KER) in a XUV-pump/IR-probe setup. To this end a theoretical model was developed describing the ionization process using Dyson Orbitals and, subsequently, the dissociation process using a large set of diabatic potential energy surfaces (PES) on which to propagate. From said set of PES, a small subset is extracted allowing for the identification of one and two photon processes chiefly responsible for the experimentally observed features.

Photoabsorption of molecular nitrogen (N₂) is investigated near the first ionization threshold using an R-matrix, multi-channel quantum defect (MQDT) approach.

We have designed a velocity map imaging (VMI) setup and integrated it with an Electrostatic Ion Beam Trap (EIBT) to study photon induced prompt and delayed electron emission from trapped cluster anions. The operational details are discussed here. The performance of the VMI is also reported for photoionization of trapped O⁻ ions.

We presents and experimental investigation on the effects produced by broad band soft X-rays (combined with a small fraction of vacuum ultra violet photons and possibly secondary elec-trons) on the surface of three moons of giant planets: Europa, Titan and Enceladus. Such environ-ments are constantly exposed to space ionizing agents (UV and soft X-rays photons, electrons and ions) allowing photodissociation processes, surface photochemistry and prebiotic chemistry. The processing of such spatial ices have promoted an enhancement in the chemical complexity, similar what may have happened in the early earth triggering the arising of life.

We present a combined experimental and theoretical study of the photodissociation of thiophene mole-cule using energy-resolved electron-ion-ion coincidence technique and self-consistent charge density functional tight-binding theory combined with a statistical approach. The observed complex molecular dynamics with many internal-energy-dependent fragmentation pathways is successfully described by the theoretical simulations.

160 nm vacuum-ultraviolet pulses generated as the 5^th harmonic of an 800 nm femtosecond laser are sufficiently energetic to drive multiphoton transitions in molecules. 2^nd order intensity- as well as interferometric autocorrelation were used as time-metrology tools for studying the photodissociation dynamics in ethylene and oxygen molecules. An imaging ion spectrometer enables the separate capture of dynamics in different fragmen-tation channels. Excitation in a non-collinear beam geometry is shown to deliver temporal resolution already in a single shot.

We present a theoretical method to extract photoelectron and nuclear kinetic energy spectra of molecules under intense ultrashort laser pulses. The method is applied to H₂⁺ photoionization and dissociation within a 3D model of the H₂⁺ molecule. This method is an extension to molecules of the resolvent technique originally proposed for atoms, which was recently implemented to extract absolute values of photoelectron and nuclear kinetic energy spectra.

Absolute rate coefficients were determined for the recurrent fluorescence (RF) process in C₆⁻ anions at excitation energies above the adiabatic electron attachment energy. The RF process is an important ingredient in understanding the formation and stabilization of anions in the interstellar medium.

New results on free OCS molecules have been obtained using Resonant X-ray Inelastic Scattering spectroscopy. A deconvolution algorithm has been applied to improve the energy resolution spectra of which we can extract detailed information on nuclear dynamics in the system.

An interface between quantum chemistry electronic structure and scattering electronic theory was developed for representing the ionization of molecules. This description is achieved by creating a mix of Gaussian and B-spline functions (GABS) for the ejected electron and standard multiconfigurational methodology for the remaining bounded ones

In this contribution, equilibrium geometries and potential energy curves computed at the CASSCF level of theory for the core hole and shake up superexcited states of small size molecules will be presented. The effect of dynamic correlation on the description of these species will be discussed based on preliminary multireference configuration interaction energetics.

A table-top electrostatic ion storage ring (μE-ring) is being developed. All the electrodes of the ring were mounted on a single rectangle plate of 480 mm × 200 mm, and 4 keV Ar⁺ ions were injected for a test of the ring. In the presentation, we will show the detailed design and the status of the μE-ring.

The "quasi-complete" basis calculation scenario for atomic excited states were extended to molecular system. We successfully construct the "quasi-complete" bases which consist of the spectroscopy orbitals determined by the key physical states and the pseudo-orbitals determined by the import electron correlations for the hydrogen molecule of H₂. By using such "quasi-complete" bases, the potential energy curves of the ground and highly excited states of the H₂ has been calculated and obtained in large scale 0 ≤ R_H-H ≤ 120 Bohr. This will be very useful for further studies on spectroscopy, photoionization and photo-dissociation processes.

A state-of-the-art photoelectron spectroscopy (PES) experimental setup is designed and built to study the structure and dynamics of interstellar medium anions, in particular polyaromatic hydrocarbon chain (PAH) anions.

Free size-selected metal clusters are investigated by core-level photoelectron spectroscopy at the free electron laser FLASH. The binding character of the clusters, as well as a multitude of relaxation channels are indicated by size- dependent core-level shifts and low-energy secondary electron emission, respectively. A new apparatus including a cryogenic ion-trap is currently built to extend the studies towards the smallest cluster sizes (less than 10 atoms), where low photo-absorption cross sections have to be matched by increased cluster density.

We study theoretically the different kinds of asymmetries that may arise in the laser-assisted photoionization of diatomic molecules.

We theoretically investigate the time-resolved photoionization of endohedral buckminsterfullerenes as probed by attosecond streaking. We show that the time delays of electrons emitted from the central atom contain the signature of confinement resonances but are also sensitive to molecular near-fields due to enhancement and screening of the probing streaking field by the C₆₀ molecule.

We have used one of the cryogenic ion storage rings of DESIREE to measure the lifetime of the ²P°_1/2 level in the sulfur anion to be 503 ± 43 seconds. This is orders of magnitude longer than any previously measured lifetime in a negatively charged ion.

Relative cross sections for photoionization and photofragmentation of endohedral fullerene Lu₃N@C₈₀^q+ (q=1,2,3) ions have been measured employing the new photon-ion spectrometer PIPE at PETRA III. Prominent structures related to the carbon K-shell ionization threshold were observed in the energy range 280 to 330 eV.

We have studied the production of neutral high-Rydberg (HR) fragments in small molecules after inner-shell excitation and ionization. Such fragments were ionized using a pulsed electric field and resulting ions were mass-analyzed with an ion time-of-flight (TOF) spectrometer. As an example, the results obtained at the C 1s ionization threshold of the methane molecule will be discussed.

Strong field ionization of small hydrocarbon chains is studied in a kinematic complete experiment using a reaction microscope. By coincidence detection of ions and electrons different ionization continua populated during the ionization process are identified. In addition, photoelectron momentum distributions from laser-aligned molecules allow to characterize the electron wavepackets emerging from different Dyson orbitals.

A novel instrument for negative-ion/positive-ion coincidence spectroscopy (NIPICO) is presented. The instrument consists of a double TOF spectrometer with a common extraction region. Electrons are deflected by means of a magnetic field. We demonstrate detections of double (NIPICO) and triple (NIPIPICO) coincidences.

We have measured the rates of neutrals produced from 10 keV C_n⁻ or C_nH⁻ (n=2, 4, 6, 8, and 10) ion beams stored in one of DESIREE's 14 K storage rings. For n=4, 6, and 8 we observe marked differences between C_n⁻ and C_nH⁻ cooling rates as inverse internal conversion [cf. S. Martin et al (2013) Phys. Rev. Lett.110, 063003] processes are effective for the C_n⁻ ions only. Knowledge of the cooling rates of these ions are important for estimates of their formation and destruction rates in cold interstellar environments.

Hydrogen-capped and methyl-capped carbon chains (polyynes) have been generated by intense femtosecond laser irradiation of pure liquid toluene. UV-Vis and Raman spectroscopy were used to confirm the presence of polyynes in the irradiated samples, and high performance liquid chromatography (HPLC) was used to separate polyynes up to C₁₈ H₂ and HC₁₃ CH₃.

We present R-matrix calculations of photoionization from NO₂, resolved in energy, angle, and both neutral and ionic state, for a range of molecular geometries, including in the vicinity of the ²A₁/²B₂ conical intersection.

Photoionization delays reveal electron dynamics on ultrashort time scales. Here, we present attosecond time-resolved experimental results of gas-phase and liquid water and we discuss the analysis methods to retrieve molecular ionization delays therefrom.

We have demonstrated a generally applicable tabletop approach utilizing a 266nm femtosecond laser pulse pump, 800nm pulse probe, coupled with Coulomb explosion imaging (CEI). We have investigated two simple chemical reactions in C₂H₂⁺ simultaneously: proton transfer and C=C bond-breaking, triggered by multiphoton ionization to excited states. Too and fro proton migration results are in excellent agreement with new ab initio trajectory simulations which predict isomerization timescales and pathways.

Prompt ionization of large biological molecules may induce ultrafast charge migration along the molecular skeleton, preceding any nuclear rearrangement. This phenomenon has been recently observed in the amino acid phenylalanine in a two-color pump probe experiment, where the production of ionic fragments was measured as a function of the time delay between the two pulses and charge fluctuations manifested as sub-4.5 fs oscillations in the quantum yield of a specific doubly charged fragment. We present our latest results in glycine, and compare with previous findings in phenylalanine. We seek to perform a systematic study including larger aminoacids such as tryptophan.

We have measured the emission spectrum of gaseous hydrogen molecules in the far ultraviolet spectral range over the large interval of excitation energies between 11 eV and 17 eV. This regime is governed by singly excited electronic states below the ionization threshold. While these features have been already investigated separately in the past, the completeness of the present measurements allows a very intuitive representation of the participating molecular effects and their respective correlations. It also contains the first complete investigation of the Condon diffraction bands visible for hydrogen through transitions into the ground state continuum.

This work presents a study of the XUV-induced ultrafast molecular dynamics of 5XU conducted with unprecedented temporal resolution. A clear dynamics occurring in 35 fs for both 5FU and 5BrU has been identified and assigned to the hydrogen migration from the C6 site to the C5 site of the molecule. Since 5XU are routinely used as radio sensitizers, the present work provides new important insights in the XUV induced structural changes responsible for the DNA breaking when these molecules are embedded in the DNA chain for radiotherapy.

We present a new method to study ion-molecule reactions at low temperatures or low collision energies and illustrate its application to the study of the H₂⁺ + H₂ → H₃⁺ + H reaction.

We present emission cross section functions for Lyman series fluorescence emission after photoexcitation of water molecules with monochromatized synchrotron radiation as function of the exciting-photon energy. Both the valence and inner-shell excitation energy range of the water molecule are covered. The results are compared to literature and contribute to complete the model of dissociative relaxation dynamics of excited small molecules.

We present a study of the vibrationally resolved B 1s photoionization cross section of the BF₃ molecule. A combination of high-resolution photoelectron spectroscopy measurements and of state-of-the-art calculations shows the evolution of the photon energy dependence of the cross section from a complete trapping of the photoelectron wave (low energies) to oscillations due to intramolecular scattering. These diffraction patterns allow to access structural information of both the neutral molecule and the core -hole species generated upon photoabsoption.

We have studied a coupled electronic-nuclear wave packet in nitric oxide using time-resolved strong-field photoelectron holography and rescattering. We show that the electronic dynamics mainly appears in the holographic structures whereas nuclear motion strongly modulates the angular distribution of the rescattered photoelectrons.

We advance high-harmonic spectroscopy to resolve molecular charge migration in time and space and simultaneously demonstrate extensive control over the process. A multidimensional approach enables us to reconstruct both quantum amplitudes and phases with a resolution of better than 100 attoseconds and to separately reconstruct field-free and laser- driven charge migration. Our techniques make charge migration in molecules measurable on the attosecond time scale and open new avenues for laser control of electronic primary processes.

Soft X-rays (50eV to 170eV) have been used in conjunction with a triple coincidence time and position sensitive detection apparatus to observe the Coulomb explosion of OCS and CS₂. By varying the X-ray energy we can access ionization channels which result in two or three body break up, for 3+, such as O⁺+C⁺+S⁺ and for 4+ such as S⁺+C⁺+S²⁺. We can compare the kinetic energy release to the value calculated for a purely Coulombic break up from near equilibrium. The extent to which channels are concerted or stepwise is also determined.

In the framework of the present work we investigate the ionization and dissociation dynamics of D₂⁺ irradiated by strong laser fields. We propose a simple three-level model, where the nuclear dynamics on the ground, dissociative, and ionization channels are considered. Our attention was focused on the calculation of ionization probability densities.

Molecular polarimetry, based on the determination of molecular frame photoemission in dissociative photoionization (DPI) studied by electron-ion coincident momentum spectroscopy, allows us to measure the complete state of elliptically polarized light. Here, we demonstrate the first complete characterization of high-order harmonic polarization state for three benchmark generation processes with inherent symmetry breaking based on the polarization of the generating beam (elliptical or counter-rotating fields) or on anisotropic targets e.g. aligned molecules. The ability to disentangle circular and unpolarized components of the XUV pulses is of particular interest to qualify the HHG sources.

We have measured the photoelectron emission and dissociation of water in the gas phase following double photoionization by a 57 eV photon. The momenta of the resulting dication ion fragments and electrons were measured in coincidence with Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS). The dissociation dynamics following the photoionization process show a marked dependence on both bond angle and kinetic energy release distribution among the fragments.

A scheme to produce ultracold hydrogen or deuterium atoms via photo-fragmentation, even allowing direct formation of a quantum gas