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We demonstrate the application of event-driven Timepix3-based detectors in combination with a double-sided velocity-map-imaging spectrometer to record the full 3D momentum of charged particles at the free-electron-laser facility FLASH. We measured the XUV induced fragmentation of $\text{N}_2$ using 250 kHz FLASH bursts with sub-pixel spatial resolution and up to 1.7~ns temporal resolution for photoelectrons. To further demonstrate the capabilities of this camera at even higher repetition rates we measured single-shot images of He($1s$) photoelectrons for bursts with a repetition rate of 1 MHz. Overall, with the Timepix3 camera we overcome limitations of standard-camera technology for advanced-imaging experiments with requirements on high event-rates and high spatio-temporal resolution.

Radiation-induced damage of biological matter is an ubiquitous problem in nature. The influence of the hydration environment is widely discussed, but its exact role remains elusive. We present the experimental observation of a hydrogen-bonded water molecule acting as a radiation protection agent for ionized pyrrole, a prototypical aromatic biomolecule. Pure samples of pyrrole and pyrrole(H$_2$O) were outer-valence ionized and the subsequent damage and relaxation processes were studied. Bare pyrrole fragmented through the breaking of the C-C or N-C covalent bonds. However, for pyrrole(H$_2$O), we observed a strong protection of the pyrrole ring through the dissociative release of neutral water or by transferring an electron or proton across the hydrogen bond. Furthermore, for pyrrole(H$_2$O) a smaller probability for double ionization was observed. Overall, a single water molecule strongly reduces the fragmentation probability and thus the persistent radiation damage of ionized pyrrole., 10 pages, 8 figures

Dissertation, University of Hamburg, 2020; Hamburg 141 pp. (2020). = Dissertation, University of Hamburg, 2020, Water is vital for the existence of life on earth, and therefore, it is dubbed as the matrix of life. Furthermore, the hydration environment plays diverse functional, structural, and dynamic roles in molecular cell biology. For instance, the photophysical and photochemical properties of UV absorbing chromophores found in biological systems are sensitive to their local solvation environment. In hydrated systems, the hydrogen-bond network between the chromophores and surrounding water molecules can provide additional relaxation pathways after excitation or ionization of chromophores, crucial for the photostability of the biological system. On the other hand, the abundant solvent environment around biological matter can enhance radiation-induced damage through, e.g., the radiolysis of water. Despite the huge efforts to unravel realistic dynamics, the role of the hydration environment upon the radiation-induced biological damage remains elusive. In the framework of this thesis, a bottom-up approach is used to systematically investigate the role of a single water molecule in the photophysics of a model chromophore, pyrrole, after ionization. This work can be divided into two main parts:the preparation of pure samples of pyrrole and microsolvated pyrrole-water in the gas phase, and a comparative photophysics investigation on these model systems utilizing time- and position- sensitive detectors. The preparation of pure and rotationally cold samples of pyrrole and pyrrole-water is achieved using a combination of a cold molecular beam and the electrostatic deflector. A knife-edge for shaping a molecular beam is implemented to improve the spatial separation of the species in a molecular beam by the electrostatic deflector as well as to reduce the contribution of atomic seed gas in the interaction zone. A pyrrole-water cluster beam with unprecedented purity of ~100 % is obtained. The extracted rotational temperature of pyrrole and pyrrole-water after the supersonic expansion is $T_\text{rot}=0.8\pm0.2$ K. Also, the number densities and rotational temperature of the cluster beam is significantly improved.In the photophysics investigation part, we mimicked radiation damage in pyrrole and pyrrole-water, after outer valence- and inner-shell ionization through strong-field ionization and site-specific x-ray ionization, respectively. In the strong-field case, single- and double- ionization of bare pyrrole resulted in fragmentation of the aromatic ring through breaking the C-C or N-C covalent bonds. Albeit, the protective effects in the cluster, a weak enhanced strong-field ionization resulting in the formation of highly charged ionic species is observed only for the pyrrole-water cluster. In the case of site-specific core-shell ionization, the fragmentation studies on bare pyrrole yielded similar channels as compared to the strong-field ionization scenario. For pyrrole-water, performing a localized x-ray ionization at the aromatic ring resulted in charge- and mass-transfer across the hydrogen-bond. Overall, a hydrogen-bonded single water molecule can facilitate radiation-protection pathways after outer valence- and inner-shell ionization of biomolecules., Published by Hamburg

MEDEA mid-term review meeting, MEDEA, Aarhus, Center for Free- Electron Laser Science, Denmark, 16 Jan 2017 - 18 Jan 2017

The journal of physical chemistry / A 123(34), 7486 - 7490 (2019). doi:10.1021/acs.jpca.9b06460, Spatial separation of water dimer from water monomer and larger water-clusters through the electric deflector is presented. A beam of water dimer with $93~\%$ purity and a rotational temperature of $1.5~$K was obtained. Following strong-field ionization using a $35~$fs laser pulse with a wavelength centered around $800~$nm and a peak intensity of $10^{14}~\text{W}/\text{cm}^2$ we observed proton transfer and $46~\%$ of the ionized water dimer broke apart into a hydronium ion $\text{H}_3\text{O}^+$ and OH., Published by ACS, Washington, DC

Chemical physics letters 721, 149 - 152 (2019). doi:10.1016/j.cplett.2019.01.052, We demonstrate the spatial separation of pyrrole and pyrrole(H$_2$O) clusters from the other atomic and molecular species in a supersonically-expanded beam of pyrrole and traces of water seeded in high-pressure helium gas. The experimental results are quantitatively supported by simulations. The obtained pyrrole(H$_2$O) cluster beam has a purity of ∼ 100 %. The extracted rotational temperature of pyrrole and pyrrole(H$_2$O) from the original supersonic expansion is $T_{rot}=$ 0.8 ± 0.2 K, whereas the temperature of the deflected, pure-pyrrole(H$_2$O) part of the molecular beam corresponds to $T_{rot}≈$ 0.4 K., Published by Elsevier, Amsterdam [u.a.]