Focused ion beam-induced deposition (FIBID) relies on controlled ion-matter interactions, but the fundamental dissociation pathways of many potential precursor molecules remain largely unexplored. In this work, we investigate the ion-induced fragmentation of the FEBID/FIBID-relevant precursor Fe(CO) _4 (acrolein) in the gas phase. Using time-of-flight mass spectrometry, we measure the fragmentation patterns resulting from collisions with He ^+ (16 keV), Ne ^+ (6 keV), and Ne ^4+ (40 keV) projectiles, covering interaction regimes from predominantly electronic stopping to higher nuclear stopping contributions. The results reveal pronounced dissociation of the ligand framework and substantial loss of functional groups, consistent with efficient energy redistribution within the metal-carbonyl core. Ne ^+ is identified as a particularly efficient projectile for inducing molecular decomposition. The data provide new insight into the stability, energy-dissipation pathways, and FIBID-relevant behaviour of Fe(CO) _4 (acrolein), offering a basis for understanding its decomposition mechanisms and comparison to other iron precursors. Schematic representation of focused ion beam-induced deposition (FIBID) and mass spectrometric analysis.

The field of attosecond physics has expanded significantly in recent years, yet experimental facilities supporting attosecond pump–attosecond probe spectroscopy remain rare. Here, we present a newly constructed beamline for the generation and application of energetic, isolated extreme ultraviolet (XUV) and soft x-ray attosecond pulses via upscaling of high-harmonic generation (HHG) in a gas medium. The fundamental properties of the HHG radiation—energy, beam profile, spectrum, and divergence—are characterized and optimized. The source delivers up to 55 nJ of pulse energy within the Zr window (65–150 eV) with high stability (∼5%–10%) and a divergence of 0.1 mrad. Numerical simulations identify optimal operating conditions consistent with experimental results. Temporal super-resolution of the driving laser is applied, resulting in a broadened spectral continuum. Furthermore, the beamline includes a split-and-delay stage before focusing the HHG radiation to a <6μm spot for pump–probe experiments using two distinct focusing optics. Spatially resolved ion microscopy is employed to trace the generated ions at the focus. The presented beamline is designed for nonlinear XUV studies with isolated attosecond pulses.

We investigate two nitrogen-containing isomers of polycyclic aromatic hydrocarbons, quinoline and isoquinoline, of composition C9H7N in collisions with 7 keV O+ and 48 keV O6+ projectile ions. By employing ion–ion coincidence mass spectrometry, we determine branching ratios for H-loss, C2H2-loss, and HCN-loss dissociation channels of Q2+ and IQ2+. The overall contribution of HCN loss is found to be the dominant decay channel. A comparison with the results of a parallel experiment on naphthalene, the simplest PAH, reveals that HCN loss in both isomers has a higher propensity than the analogous C2H2 loss of naphthalene. The positional identity of the nitrogen atom in the two isomers mainly manifests in many-body fragmentation of their dications. Potential energy surfaces of Q2+ and IQ2+ are further computed to explore complete fragmentation mechanisms. Parent dications (Q2+ and IQ2+) are identified to isomerize via seven-membered ring structures before elimination of C2H2 and HCN. While prompt dissociation is the primary pathway, the dominant channel of each neutral-loss class also exhibits delayed fragmentation.

The present work is a continuation of our studies with iron pentacarbonyl, a model organometallic precursor for Focused Ion Beam-Induced Deposition (FIBID). Interactions of He2+(16 keV), Ne+(6 keV), Ne4+(40 keV), Ar2+(12 keV) and Ar8+(64 keV) projectile ions with [Fe(CO)5]n clusters are studied using TOF mass spectrometry. The clusters represent an intermediate between the gas phase and the bulk environment and can be used as a proxy for the processes in complex environments such as e.g. the nanostructure deposition. The addition of environment in the present study results in the observation of fragments with high kinetic energies ejected from clusters, an overall reduction of the fragmentation, and observation of a range of fragments associated with C-O bond dissociation, not observed for isolated molecules. On the other hand, the high efficiency of the Ne+ projectile in fragmenting the Fe(CO)5 isolated molecule is also observed in clusters.

We present an investigation of the ultrafast dynamics of the polycyclic aromatic hydrocarbon fluorene initiated by an intense femtosecond near- infrared laser pulse (810 nm) and probed by a weak visible pulse (405 nm). Using a multichannel detection scheme (mass spectra, electron and ion velocity-map imaging), we provide a full disentanglement of the complex dynamics of the vibronically excited parent molecule, its excited ionic states, and fragments. We observed various channels resulting from the strong-field ionization regime. In particular, we observed the formation of the unstable tetracation of fluorene, above-threshold ionization features in the photoelectron spectra, and evidence of ubiquitous secondary fragmentation. We produced a global fit of all observed time-dependent photoelectron and photoion channels. This global fit includes four parent ions extracted from the mass spectra, 15 kinetic-energy-resolved ionic fragments extracted from ion velocity map imaging, and five photoelectron channels obtained from electron velocity map imaging. The fit allowed for the extraction of 60 lifetimes of various metastable photoinduced intermediates.

We have investigated the fragmentation dynamics of the organometallic ferrocene molecule after interaction with multiply charged ions using multicoincidence mass spectrometry and quantum chemistry calculations. We observed unexpected fragmentation dynamics of the two-body breakup channels from ferrocene dications revealing a charge screening effect from the iron atom and delayed fragmentation dynamics. These observations are rationalized through the population of a specific long-lived excited state, where one positive charge is located on each cyclopentadienyl ring. Combined experiment/theory study on ionized ferrocene molecules. We found that, due to the population of a specific long-lived excited state, charge screening effects from the iron atom and delayed fragmentations occur leading to unexpected dynamics.

Rabi oscillations, a prominent feature of coherent light-matter interaction arise when a two-level system interacts periodically with an external electromagnetic field [1]. Despite being a cornerstone in quantum physics, they are usually studied in the long-wavelength region, ranging from mid-infrared to visible. Here, we demonstrate that intense femtosecond extreme-ultraviolet (XUV) pulses from FERMI seeded free-electron laser [2] can drive Rabi oscillations between the two levels: 1s 2 and 1s4p in helium.

Adamantane, the smallest diamondoid molecule with a symmetrical cage, contains two distinct carbon sites, CH and CH2. The ionization/excitation of the molecule leads to the cage opening and strong structural reorganization. While theoretical predictions suggest that the carbon site CH primarily causes the cage opening, the role of the other CH2 site remains unclear. In this study, we used advanced experimental Auger electron–ion coincidence techniques and theoretical calculations to investigate the fragmentation dynamics of adamantane after resonant inner-shell photoexcitation. Our results demonstrate that some fragmentation channels exhibit site-sensitivity of the initial core–hole location, indicating that different carbon site excitations could lead to unique cage opening mechanisms.

The valence ionization of uracil and mixed water-uracil clusters has been studied experimentally and by ab initio calculations. In both measurements, the spectrum onset shows a red shift with respect to the uracil molecule, with the mixed cluster characterized by peculiar features unexplained by the sum of independent contributions of the water or uracil aggregation. To interpret and assign all the contributions, we performed a series of multi-level calculations, starting from an exploration of several cluster structures using automated conformer-search algorithms based on a tight-binding approach. Ionization energies have been assessed on smaller clusters via a comparison between accurate wavefunction-based approaches and cost-effective DFT-based simulations, the latter of which were applied to clusters up to 12 uracil and 36 water molecules. The results confirm that (i) the bottom-up approach based on a multilevel method [Mattioli et al. Phys. Chem. Chem. Phys. 23, 1859 (2021)] to the structure of neutral clusters of unknown experimental composition converges to precise structure-property relationships and (ii) the coexistence of pure and mixed clusters in the water-uracil samples. A natural bond orbital (NBO) analysis performed on a subset of clusters highlighted the special role of H-bonds in the formation of the aggregates. The NBO analysis yields second-order perturbative energy between the H-bond donor and acceptor orbitals correlated with the calculated ionization energies. This sheds light on the role of the oxygen lone-pairs of the uracil CO group in the formation of strong H-bonds, with a stronger directionality in mixed clusters, giving a quantitative explanation for the formation of core-shell structures.

Copper-thiolate self-assembly nanostructures are a unique class of nanomaterials because of their interesting properties such as hierarchical structures, luminescence, and large nonlinear optical efficiency. Herein, we synthesized biomolecule cysteine (Cys) and glutathione (GSH) capped sub-100 nm self-assembly nanoparticles (Cu-Cys-GSH NPs) with red fluorescence. The as-synthesized NPs show high emission enhancement in the presence of ethanol, caused by the aggregation-induced emission. We correlated the structure and optical properties of Cu-Cys-GSH NPs by measuring the mass, morphology, and surface charge as well as their two-photon excited fluorescence cross-section (σ2PEPL), two-photon absorption cross-section (σTPA) and first hyperpolarizability (β) of Cu-Cys-GSH NPs in water and water-ethanol using near-infrared wavelength. We found a high β value as (77 ± 10) × 10-28 esu (in water) compared to the reference medium water. The estimated values of σ2PEPL and σTPA are found to be (13 ± 2) GM and (1.4 ± 0.2) × 104 GM, respectively. We hope our investigations of linear and nonlinear optical properties of copper-thiolate self-assemblies in water and its solvent-induced aggregates will open up new possibilities in designing self-assembled systems for many applications including sensing, drug delivery, and catalysis.

Photodissociation molecular dynamics of gas-phase 2,5-diiodothiophene molecules was studied in an electron-energy-resolved electron-multi-ion coincidence experiment performed at the FinEstBeAMS beamline of MAX IV synchrotron. Following the photoionization of the iodine 4d subshell and the Auger decay, the dissociation landscape of the molecular dication was investigated as a function of the Auger electron energy. Concentrating on an major dissociation pathway, C4H2I2S2+ → C4H2S+ + I+ + I, and accessing the timescales of the process via ion momentum correlation analysis, it was revealed how this three-body process changes depending on the available internal energy. Using a generalized secondary dissociation model, the process was shown to evolve from secondary dissociation regime towards concerted dissociation as the available energy increased, with the secondary dissociation time constant changing from 1.5 ps to 129 fs. The experimental results were compared with simulations using a stochastic charge-hopping molecular mechanics model. It represented the observed trend and also gave a fair quantitative agreement with the experiment.

The XUV beams generated via high order harmonic generation (HHG) in gases have spatial properties evolving with the harmonic order. It leads to chromatic aberrations when the harmonics are focussed so that, locally, the spectral content can change significantly during propagation [1]–[3] especially near focus.

Attosecond pulses created by high-order harmonic generation in gases often exhibit strong chromatic aberrations, arising from the broad bandwidth and wavelength-dependent nonlinear light-matter interaction. When the driving laser intensity varies spatially, as for Gaussian driving beams, the apparent source position of the harmonics differs significantly from one order to the next, thus affecting the achievable intensity and duration of the attosecond pulses when they are focused on a target. We show that these chromatic aberrations can be reduced by spatially shaping the fundamental beam to generate high-order harmonics with a driver having a flat-top profile inside the gas medium. By measuring both the intensity profile and wavefront for each harmonic in a plane, we access the extreme ultra-violet (XUV) beam properties and investigate these properties near focus. We observe that controlling chromatic aberrations by flat-top spatial shaping strongly reduces the variation of the XUV spectrum on the beam axis during propagation and, in return, the longitudinal sensitivity of both the temporal profiles and the temporal shifts of the focused attosecond pulses.

We investigated the dissociation of dications and trications of three polycyclic aromatic hydrocarbons (PAHs), fluorene, phenanthrene, and pyrene. PAHs are a family of molecules ubiquitous in space and involved in much of the chemistry of the interstellar medium. In our experiments, ions are formed by interaction with 30.3 nm extreme ultraviolet (XUV) photons, and their velocity map images are recorded using a PImMS2 multi-mass imaging sensor. Application of recoil-frame covariance analysis allows the total kinetic energy release (TKER) associated with multiple fragmentation channels to be determined to high precision, ranging 1.94-2.60 eV and 2.95-5.29 eV for the dications and trications, respectively. Experimental measurements are supported by Born-Oppenheimer molecular dynamics (BOMD) simulations.

Rabi oscillations are periodic modulations of populations in two-level systems interacting with a time-varying field 1 . They are ubiquitous in physics with applications in different areas such as photonics 2 , nano-electronics 3 , electron microscopy 4 and quantum information 5 . While the theory developed by Rabi was intended for fermions in gyrating magnetic fields, Autler and Townes realized that it could also be used to describe coherent light–matter interactions within the rotating-wave approximation 6 . Although intense nanometre-wavelength light sources have been available for more than a decade 7 – 9 , Rabi dynamics at such short wavelengths has not been directly observed. Here we show that femtosecond extreme-ultraviolet pulses from a seeded free-electron laser 10 can drive Rabi dynamics between the ground state and an excited state in helium atoms. The measured photoelectron signal reveals an Autler–Townes doublet and an avoided crossing, phenomena that are both fundamental to coherent atom–field interactions 11 . Using an analytical model derived from perturbation theory on top of the Rabi model, we find that the ultrafast build-up of the doublet structure carries the signature of a quantum interference effect between resonant and non-resonant photoionization pathways. Given the recent availability of intense attosecond 12 and few-femtosecond 13 extreme-ultraviolet pulses, our results unfold opportunities to carry out ultrafast manipulation of coherent processes at short wavelengths using free-electron lasers.

The ultraviolet (UV)-induced dissociation and photofragmentation of gas-phase CH 2 BrI molecules induced by intense femtosecond extreme ultraviolet (XUV) pulses at three different photon energies are studied by multi-mass ion imaging. Using a UV-pump–XUV-probe scheme, charge transfer between highly charged iodine ions and neutral CH 2 Br radicals produced by C–I bond cleavage is investigated. In earlier charge-transfer studies, the center of mass of the molecules was located along the axis of the bond cleaved by the pump pulse. In the present case of CH 2 BrI, this is not the case, thus inducing a rotation of the fragment. We discuss the influence of the rotation on the charge transfer process using a classical over-the-barrier model. Our modeling suggests that, despite the fact that the dissociation is slower due to the rotational excitation, the critical interatomic distance for charge transfer is reached faster. Furthermore, we suggest that charge transfer during molecular fragmentation may be modulated in a complex way.

We report on the use of extreme ultraviolet (XUV, 30.3 nm) radiation from the Free-electron LASer in Hamburg (FLASH) and visible (Vis, 405 nm) photons from an optical laser to investigate the relaxation and fragmentation dynamics of fluorene ions. The ultrashort laser pulses allow to resolve the molecular processes occurring on the femtosecond timescales. Fluorene is a prototypical small polycyclic aromatic hydrocarbon (PAH). Through their infrared emission signature, PAHs have been shown to be ubiquitous in the universe, and they are assumed to play an important role in the chemistry of the interstellar medium. Our experiments track the ionization and dissociative ionization products of fluorene through time-of-flight mass spectrometry and velocity-map imaging. Multiple processes involved in the formation of each of the fragment ions are disentangled through analysis of the ion images. The relaxation lifetimes of the excited fluorene monocation and dication obtained through the fragment formation channels are reported to be in the range of a few tens of femtoseconds to a few picoseconds.

We investigate the fragmentation dynamics of adamantane dications produced after core-ionization at the carbon edge followed by Auger decay. The combination of high-resolution electron spectroscopy, energy-resolved electron-ion multi-coincidence spectroscopy and different theoretical models allows us to give a complete characterization of the processes involved after ionization. We show that energy- and site-sensitivity is observed even for a highly-symmetric molecule that lacks any unique atomic site.

We study resonant two-photon ionization of helium atoms via the 1s3p, 1s4p and 1s5p 1P1 states using the 15th harmonic of a titanium-sapphire laser for the excitation and a weak fraction of the laser field for the ionization. The phase of the photoelectron wavepackets is measured by an attosecond interferometric technique, using the 17th harmonic. We perform experiments with angular resolution using a velocity map imaging spectrometer and with high energy resolution using a magnetic bottle electron spectrometer. Our results are compared to calculations using the two-photon random phase approximation with exchange to account for electron correlation effects. We give an interpretation for the multiple π-rad phase jumps observed, both at and away from resonance, as well as their dependence on the emission angle.