@article{MetjeLeverMayeretal.2020, author = {Metje, Jan and Lever, Fabiano and Mayer, Dennis and Squibb, Richard James and Robinson, Matthew Scott and Niebuhr, Mario and Feifel, Raimund and D{\"u}sterer, Stefan and G{\"u}hr, Markus}, title = {URSA-PQ}, series = {Applied Sciences}, volume = {10}, journal = {Applied Sciences}, number = {21}, publisher = {MDPI}, address = {Basel}, issn = {2076-3417}, doi = {10.3390/app10217882}, pages = {13}, year = {2020}, abstract = {We present a highly flexible and portable instrument to perform pump-probe spectroscopy with an optical and an X-ray pulse in the gas phase. The so-called URSA-PQ (German for 'Ultraschnelle R{\"o}ntgenspektroskopie zur Abfrage der Photoenergiekonversion an Quantensystemen', Engl. 'ultrafast X-ray spectroscopy for probing photoenergy conversion in quantum systems') instrument is equipped with a magnetic bottle electron spectrometer (MBES) and tools to characterize the spatial and temporal overlap of optical and X-ray laser pulses. Its adherence to the CAMP instrument dimensions allows for a wide range of sample sources as well as other spectrometers to be included in the setup. We present the main design and technical features of the instrument. The MBES performance was evaluated using Kr M4,5NN Auger lines using backfilled Kr gas, with an energy resolution ΔE/E ≅ 1/40 in the integrating operative mode. The time resolution of the setup at FLASH 2 FL 24 has been characterized with the help of an experiment on 2-thiouracil that is inserted via the instruments' capillary oven. We find a time resolution of 190 fs using the molecular 2p photoline shift and attribute this to different origins in the UV-pump—the X-ray probe setup.}, language = {en} } @misc{MetjeLeverMayeretal.2020, author = {Metje, Jan and Lever, Fabiano and Mayer, Dennis and Squibb, Richard James and Robinson, Matthew Scott and Niebuhr, Mario and Feifel, Raimund and D{\"u}sterer, Stefan and G{\"u}hr, Markus}, title = {URSA-PQ}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, number = {1016}, issn = {1866-8372}, doi = {10.25932/publishup-48307}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-483073}, pages = {15}, year = {2020}, abstract = {We present a highly flexible and portable instrument to perform pump-probe spectroscopy with an optical and an X-ray pulse in the gas phase. The so-called URSA-PQ (German for 'Ultraschnelle R{\"o}ntgenspektroskopie zur Abfrage der Photoenergiekonversion an Quantensystemen', Engl. 'ultrafast X-ray spectroscopy for probing photoenergy conversion in quantum systems') instrument is equipped with a magnetic bottle electron spectrometer (MBES) and tools to characterize the spatial and temporal overlap of optical and X-ray laser pulses. Its adherence to the CAMP instrument dimensions allows for a wide range of sample sources as well as other spectrometers to be included in the setup. We present the main design and technical features of the instrument. The MBES performance was evaluated using Kr M4,5NN Auger lines using backfilled Kr gas, with an energy resolution ΔE/E ≅ 1/40 in the integrating operative mode. The time resolution of the setup at FLASH 2 FL 24 has been characterized with the help of an experiment on 2-thiouracil that is inserted via the instruments' capillary oven. We find a time resolution of 190 fs using the molecular 2p photoline shift and attribute this to different origins in the UV-pump—the X-ray probe setup.}, language = {en} } @misc{Guehr2016, author = {G{\"u}hr, Markus}, title = {Ultrafast Soft X-ray Probing of Gas Phase Molecular Dynamics}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-97215}, year = {2016}, abstract = {The molecular ability to selectively and efficiently convert sunlight into other forms of energy like heat, bond change, or charge separation is truly remarkable. The decisive steps in these transformations often happen on a femtosecond timescale and require transitions among different electronic states that violate the Born-Oppenheimer approximation (BOA). Non-BOA transitions pose challenges to both theory and experiment. From a theoretical point of view, excited state dynamics and nonadiabatic transitions both are difficult problems (see Figure 1(a)). However, the theory on non-BOA dynamics has advanced significantly over the last two decades. Full dynamical simulations for molecules of the size of nucleobases have been possible for a couple of years and allow predictions of experimental observables like photoelectron energy or ion yield. The availability of these calculations for isolated molecules has spurred new experimental efforts to develop methods that are sufficiently different from all optical techniques. For determination of transient molecular structure, femtosecond X-ray diffraction and electron diffraction have been implemented on optically excited molecules.}, language = {en} } @article{RobinsonNiebuhrLeveretal.2021, author = {Robinson, Matthew Scott and Niebuhr, Mario and Lever, Fabiano and Mayer, Dennis and Metje, Jan and G{\"u}hr, Markus}, title = {Ultrafast photo-ion probing of the ring-opening process in trans-stilbene oxide}, series = {Chemistry - a European journal}, volume = {27}, journal = {Chemistry - a European journal}, number = {44}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1521-3765}, doi = {10.1002/chem.202101343}, pages = {11418 -- 11427}, year = {2021}, abstract = {The ultrafast photo-induced ring opening of the oxirane derivative trans-stilbene oxide has been studied through the use of ultrafast UV/UV pump-probe spectroscopy by using photo-ion detection. Single- and multiphoton probe paths and final states were identified through comparisons between UV power studies and synchrotron-based vacuum ultraviolet (VUV) single-photon ionization studies. Three major time-dependent features of the parent ion (sub-450 fs decay, (1.5 +/- 0.2) ps, and >100 ps) were observed. These decays are discussed in conjunction with the primary ring-opening mechanism of stilbene oxide, which occurs through C-C dissociation in the oxirane ring. The appearance of fragments relating to the masses of dehydrogenated diphenylmethane (167 amu) and dehydrogenated methylbenzene (90 amu) were also investigated. The appearance of the 167 amu fragment could suggest an alternative ultrafast ring-opening pathway via the dissociation of one of the C-O bonds within the oxirane ring.}, language = {en} } @article{XiongMignoletFangetal.2017, author = {Xiong, Hui and Mignolet, Benoit and Fang, Li and Osipov, Timur and Wolf, Thomas J. A. and Sistrunk, Emily and G{\"u}hr, Markus and Remacle, Francoise and Berrah, Nora}, title = {The Role of Super-Atom Molecular Orbitals in Doped Fullerenes in a Femtosecond Intense Laser Field}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-00124-9}, pages = {8}, year = {2017}, abstract = {The interaction of gas phase endohedral fullerene Ho3N@C-80 with intense (0.1-5 x 10(14) W/cm(2)), short (30 fs), 800 nm laser pulses was investigated. The power law dependence of Ho3N@C-80(q+), q = 1-2, was found to be different from that of C-60. Time-dependent density functional theory computations revealed different light-induced ionization mechanisms. Unlike in C-60, in doped fullerenes, the breaking of the cage spherical symmetry makes super atomic molecular orbital (SAMO) states optically active. Theoretical calculations suggest that the fast ionization of the SAMO states in Ho3N@C-80 is responsible for the n = 3 power law for singly charged parent molecules at intensities lower than 1.2 x 10(14) W/cm(2).}, language = {en} } @article{WolfSanchezYangetal.2019, author = {Wolf, Thomas J. A. and Sanchez, David M. and Yang, J. and Parrish, R. M. and Nunes, J. P. F. and Centurion, M. and Coffee, R. and Cryan, J. P. and G{\"u}hr, Markus and Hegazy, Kareem and Kirrander, Adam and Li, R. K. and Ruddock, J. and Shen, Xiaozhe and Vecchione, T. and Weathersby, S. P. and Weber, Peter M. and Wilkin, K. and Yong, Haiwang and Zheng, Q. and Wang, X. J. and Minitti, Michael P. and Martinez, Todd J.}, title = {The photochemical ring-opening of 1,3-cyclohexadiene imaged by ultrafast electron diffraction}, series = {Nature chemistry}, volume = {11}, journal = {Nature chemistry}, number = {6}, publisher = {Nature Publ. Group}, address = {London}, issn = {1755-4330}, doi = {10.1038/s41557-019-0252-7}, pages = {504 -- 509}, year = {2019}, abstract = {The ultrafast photoinduced ring-opening of 1,3-cyclohexadiene constitutes a textbook example of electrocyclic reactions in organic chemistry and a model for photobiological reactions in vitamin D synthesis. Although the relaxation from the photoexcited electronic state during the ring-opening has been investigated in numerous studies, the accompanying changes in atomic distance have not been resolved. Here we present a direct and unambiguous observation of the ring-opening reaction path on the femtosecond timescale and subangstrom length scale using megaelectronvolt ultrafast electron diffraction. We followed the carbon-carbon bond dissociation and the structural opening of the 1,3-cyclohexadiene ring by the direct measurement of time-dependent changes in the distribution of interatomic distances. We observed a substantial acceleration of the ring-opening motion after internal conversion to the ground state due to a steepening of the electronic potential gradient towards the product minima. The ring-opening motion transforms into rotation of the terminal ethylene groups in the photoproduct 1,3,5-hexatriene on the subpicosecond timescale.}, language = {en} } @article{YoungUedaGuehretal.2018, author = {Young, Linda and Ueda, Kiyoshi and G{\"u}hr, Markus and Bucksbaum, Philip H. and Simon, Marc and Mukamel, Shaul and Rohringer, Nina and Prince, Kevin C. and Masciovecchio, Claudio and Meyer, Michael and Rudenko, Artem and Rolles, Daniel and Bostedt, Christoph and Fuchs, Matthias and Reis, David A. and Santra, Robin and Kapteyn, Henry and Murnane, Margaret and Ibrahim, Heide and Legare, Francois and Vrakking, Marc and Isinger, Marcus and Kroon, David and Gisselbrecht, Mathieu and W{\"o}rner, Hans Jakob and Leone, Stephen R.}, title = {Roadmap of ultrafast x-ray atomic and molecular physics}, series = {Journal of physics : B, Atomic, molecular and optical physics}, volume = {51}, journal = {Journal of physics : B, Atomic, molecular and optical physics}, number = {3}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0953-4075}, doi = {10.1088/1361-6455/aa9735}, pages = {45}, year = {2018}, abstract = {X-ray free-electron lasers (XFELs) and table-top sources of x-rays based upon high harmonic generation (HHG) have revolutionized the field of ultrafast x-ray atomic and molecular physics, largely due to an explosive growth in capabilities in the past decade. XFELs now provide unprecedented intensity (10(20) W cm(-2)) of x-rays at wavelengths down to similar to 1 Angstrom, and HHG provides unprecedented time resolution (similar to 50 attoseconds) and a correspondingly large coherent bandwidth at longer wavelengths. For context, timescales can be referenced to the Bohr orbital period in hydrogen atom of 150 attoseconds and the hydrogen-molecule vibrational period of 8 femtoseconds; wavelength scales can be referenced to the chemically significant carbon K-edge at a photon energy of similar to 280 eV (44 Angstroms) and the bond length in methane of similar to 1 Angstrom. With these modern x-ray sources one now has the ability to focus on individual atoms, even when embedded in a complex molecule, and view electronic and nuclear motion on their intrinsic scales (attoseconds and Angstroms). These sources have enabled coherent diffractive imaging, where one can image non-crystalline objects in three dimensions on ultrafast timescales, potentially with atomic resolution. The unprecedented intensity available with XFELs has opened new fields of multiphoton and nonlinear x-ray physics where behavior of matter under extreme conditions can be explored. The unprecedented time resolution and pulse synchronization provided by HHG sources has kindled fundamental investigations of time delays in photoionization, charge migration in molecules, and dynamics near conical intersections that are foundational to AMO physics and chemistry. This roadmap coincides with the year when three new XFEL facilities, operating at Angstrom wavelengths, opened for users (European XFEL, Swiss-FEL and PAL-FEL in Korea) almost doubling the present worldwide number of XFELs, and documents the remarkable progress in HHG capabilities since its discovery roughly 30 years ago, showcasing experiments in AMO physics and other applications. Here we capture the perspectives of 17 leading groups and organize the contributions into four categories: ultrafast molecular dynamics, multidimensional x-ray spectroscopies; high-intensity x-ray phenomena; attosecond x-ray science.}, language = {en} } @misc{YoungUedaGuehretal.2018, author = {Young, Linda and Ueda, Kiyoshi and G{\"u}hr, Markus and Bucksbaum, Philip H. and Simon, Marc and Mukamel, Shaul and Rohringer, Nina and Prince, Kevin C. and Masciovecchio, Claudio and Meyer, Michael and Rudenko, Artem and Rolles, Daniel and Bostedt, Christoph and Fuchs, Matthias and Reis, David A. and Santra, Robin and Kapteyn, Henry and Murnane, Margaret and Ibrahim, Heide and L{\´e}gar{\´e}, Fran{\c{c}}ois and Vrakking, Marc and Isinger, Marcus and Kroon, David and Gisselbrecht, Mathieu and L'Huillier, Anne and W{\"o}rner, Hans Jakob and Leone, Stephen R.}, title = {Roadmap of ultrafast x-ray atomic and molecular physics}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {668}, issn = {1866-8372}, doi = {10.25932/publishup-42423}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-424238}, pages = {46}, year = {2018}, abstract = {X-ray free-electron lasers (XFELs) and table-top sources of x-rays based upon high harmonic generation (HHG) have revolutionized the field of ultrafast x-ray atomic and molecular physics, largely due to an explosive growth in capabilities in the past decade. XFELs now provide unprecedented intensity (1020 W cm-2) of x-rays at wavelengths down to ~1 {\AA}ngstrom, and HHG provides unprecedented time resolution (~50 attoseconds) and a correspondingly large coherent bandwidth at longer wavelengths. For context, timescales can be referenced to the Bohr orbital period in hydrogen atom of 150 attoseconds and the hydrogen-molecule vibrational period of 8 femtoseconds; wavelength scales can be referenced to the chemically significant carbon K-edge at a photon energy of ~280 eV (44 {\AA}ngstroms) and the bond length in methane of ~1 {\AA}ngstrom. With these modern x-ray sources one now has the ability to focus on individual atoms, even when embedded in a complex molecule, and view electronic and nuclear motion on their intrinsic scales (attoseconds and {\AA}ngstroms). These sources have enabled coherent diffractive imaging, where one can image non-crystalline objects in three dimensions on ultrafast timescales, potentially with atomic resolution. The unprecedented intensity available with XFELs has opened new fields of multiphoton and nonlinear x-ray physics where behavior of matter under extreme conditions can be explored. The unprecedented time resolution and pulse synchronization provided by HHG sources has kindled fundamental investigations of time delays in photoionization, charge migration in molecules, and dynamics near conical intersections that are foundational to AMO physics and chemistry. This roadmap coincides with the year when three new XFEL facilities, operating at {\AA}ngstrom wavelengths, opened for users (European XFEL, Swiss-FEL and PAL-FEL in Korea) almost doubling the present worldwide number of XFELs, and documents the remarkable progress in HHG capabilities since its discovery roughly 30 years ago, showcasing experiments in AMO physics and other applications. Here we capture the perspectives of 17 leading groups and organize the contributions into four categories: ultrafast molecular dynamics, multidimensional x-ray spectroscopies; high-intensity x-ray phenomena; attosecond x-ray science.}, language = {en} } @article{WolfGuehr2019, author = {Wolf, Thomas and G{\"u}hr, Markus}, title = {Photochemical pathways in nucleobases measured with an X-ray FEL}, series = {Philosophical Transactions of the Royal Society of London, Series A : Mathematical, Physical and Engineering Sciences}, volume = {377}, journal = {Philosophical Transactions of the Royal Society of London, Series A : Mathematical, Physical and Engineering Sciences}, number = {2145}, publisher = {Royal Society}, address = {London}, issn = {1364-503X}, doi = {10.1098/rsta.2017.0473}, pages = {12}, year = {2019}, abstract = {The conversion of light energy into other molecular energetic degrees of freedom is often dominated by ultrafast, non-adiabatic processes. Femtosecond spectroscopy with optical pulses has helped in shaping our understanding of crucial processes in molecular energy-conversion. The advent of new, ultrashort and bright X-ray free electron laser sources opens the possibility to use X-ray-typical element and site sensitivity for ultrafast molecular research. We present two types of spectroscopy, ultrafast Auger and ultrafast X-ray absorption spectroscopy, and discuss their sensitivity to molecular processes. While Auger spectroscopy is able to monitor bond distance changes in the vicinity of an X-ray created core hole, near-edge absorption spectroscopy can deliver high-fidelity information on non-adiabatic transitions involving lone-pair orbitals. We demonstrate these features on the example of the UV-excited nucleobase thymine, investigated at the oxygen K-edge. We find a C-O bond elongation in the Auger data in addition to pi pi*/n pi* non-adiabatic transition in X-ray near-edge absorption. We compare the results from both methods and draw a conclusive scenario of non-adiabatic molecular relaxation after UV excitation.}, language = {en} } @article{WolfHolzmeierWagneretal.2017, author = {Wolf, Thomas J. A. and Holzmeier, Fabian and Wagner, Isabella and Berrah, Nora and Bostedt, Christoph and Bozek, John and Bucksbaum, Phil and Coffee, Ryan and Cryan, James and Farrell, Joe and Feifel, Raimund and Martinez, Todd J. and McFarland, Brian and Mucke, Melanie and Nandi, Saikat and Tarantelli, Francesco and Fischer, Ingo and G{\"u}hr, Markus}, title = {Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra}, series = {Applied sciences}, volume = {7}, journal = {Applied sciences}, number = {7}, publisher = {MDPI}, address = {Basel}, issn = {2076-3417}, doi = {10.3390/app7070681}, pages = {11}, year = {2017}, abstract = {Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymines neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.}, language = {en} } @article{WolfHolzmeierWagneretal.2017, author = {Wolf, Thomas J. A. and Holzmeier, Fabian and Wagner, Isabella and Berrah, Nora and Bostedt, Christoph and Bozek, John and Bucksbaum, Philip H. and Coffee, Ryan and Cryan, James and Farrell, Joe and Feifel, Raimund and Martinez, Todd J. and McFarland, Brian and Mucke, Melanie and Nandi, Saikat and Tarantelli, Francesco and Fischer, Ingo and G{\"u}hr, Markus}, title = {Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra}, series = {Applied Sciences}, volume = {7}, journal = {Applied Sciences}, number = {7}, publisher = {MDPI}, address = {Basel}, issn = {2076-3417}, doi = {10.3390/app7070681}, year = {2017}, abstract = {Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine′s neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.}, language = {en} } @misc{WolfHolzmeierWagneretal.2017, author = {Wolf, Thomas J. A. and Holzmeier, Fabian and Wagner, Isabella and Berrah, Nora and Bostedt, Christoph and Bozek, John and Bucksbaum, Philip H. and Coffee, Ryan and Cryan, James and Farrell, Joe and Feifel, Raimund and Martinez, Todd J. and McFarland, Brian and Mucke, Melanie and Nandi, Saikat and Tarantelli, Francesco and Fischer, Ingo and G{\"u}hr, Markus}, title = {Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402692}, pages = {11}, year = {2017}, abstract = {Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine′s neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.}, language = {en} } @article{WolfParrishMyhreetal.2019, author = {Wolf, Thomas J. A. and Parrish, Robert M. and Myhre, Rolf H. and Martinez, Todd J. and Koch, Henrik and G{\"u}hr, Markus}, title = {Observation of Ultrafast Intersystem Crossing in Thymine by Extreme Ultraviolet Time-Resolved Photoelectron Spectroscopy}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {123}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {32}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.9b05573}, pages = {6897 -- 6903}, year = {2019}, abstract = {We studied the photoinduced ultrafast relaxation dynamics of the nucleobase thymine using gas-phase time-resolved photoelectron spectroscopy. By employing extreme ultraviolet pulses from high harmonic generation for photoionization, we substantially extend our spectral observation window with respect to previous studies. This enables us to follow relaxation of the excited state population all the way to low-lying electronic states including the ground state. In thymine, we observe relaxation from the optically bright (1)pi pi* state of thymine to a dark (1)n pi* state within 80 +/- 30 fs. The (1)n pi* state relaxes further within 3.5 +/- 0.3 ps to a low-lying electronic state. By comparison with quantum chemical simulations, we can unambiguously assign its spectroscopic signature to the (3)pi pi* state. Hence, our study draws a comprehensive picture of the relaxation mechanism of thymine including ultrafast intersystem crossing to the triplet manifold.}, language = {en} } @article{HolzmeierWolfGiengeretal.2018, author = {Holzmeier, Fabian and Wolf, Thomas J. A. and Gienger, Christian and Wagner, Isabella and Bozek, J. and Nandi, S. and Nicolas, C. and Fischer, Ingo and G{\"u}hr, Markus and Fink, Reinhold F.}, title = {Normal and resonant Auger spectroscopy of isocyanic acid, HNCO}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {149}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {3}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.5030621}, pages = {13}, year = {2018}, abstract = {In this paper, we investigate HNCO by resonant and nonresonant Auger electron spectroscopy at the K-edges of carbon, nitrogen, and oxygen, employing soft X-ray synchrotron radiation. In comparison with the isosteric but linear CO2 molecule, spectra of the bent HNCO molecule are similar but more complex due to its reduced symmetry, wherein the degeneracy of the π-orbitals is lifted. Resonant Auger electron spectra are presented at different photon energies over the first core-excited 1s → 10a′ resonance. All Auger electron spectra are assigned based on ab initio configuration interaction computations combined with the one-center approximation for Auger intensities and moment theory to consider vibrational motion. The calculated spectra were scaled by a newly introduced energy scaling factor, and generally, good agreement is found between experiment and theory for normal as well as resonant Auger electron spectra. A comparison of resonant Auger spectra with nonresonant Auger structures shows a slight broadening as well as a shift of the former spectra between -8 and -9 eV due to the spectating electron. Since HNCO is a small molecule and contains the four most abundant atoms of organic molecules, the reported Auger electron decay spectra will provide a benchmark for further theoretical approaches in the computation of core electron spectra.}, language = {en} } @misc{GessnerGuehr2016, author = {Gessner, Oliver and G{\"u}hr, Markus}, title = {Monitoring Ultrafast Chemical Dynamics by Time-Domain X-ray Photo- and Auger-Electron Spectroscopy}, series = {Accounts of chemical research}, volume = {49}, journal = {Accounts of chemical research}, publisher = {American Chemical Society}, address = {Washington}, issn = {0001-4842}, doi = {10.1021/acs.accounts.5b00361}, pages = {138 -- 145}, year = {2016}, abstract = {The directed flow of charge and energy is at the heart of all chemical processes. Extraordinary efforts are underway to monitor and understand the concerted motion of electrons and nuclei with ever increasing spatial and temporal sensitivity. The element specificity, chemical sensitivity, and temporal resolution of ultrafast X-ray spectroscopy techniques hold great promise to provide new insight into the fundamental interactions underlying chemical dynamics in systems ranging from isolated molecules to application-like devices. Here, we focus on the potential of ultrafast X-ray spectroscopy techniques based on the detection of photo- and Auger electrons to provide new fundamental insight into photochemical processes of systems with various degrees of complexity. Isolated nucleobases provide an excellent testing ground for our most fundamental understanding of intramolecular coupling between electrons and nuclei beyond the traditionally applied Born-Oppenheimer approximation. Ultrafast electronic relaxation dynamics enabled by the breakdown of this approximation is the major component of the nucleobase photoprotection mechanisms. Transient X-ray induced Auger electron spectroscopy on photoexcited thymine molecules provides atomic-site specific details of the extremely efficient coupling that converts potentially bond changing ultraviolet photon energy into benign heat. In particular, the time-dependent spectral shift of a specific Auger band is sensitive to the length of a single bond within the molecule. The X-ray induced Auger transients show evidence for an electronic transition out of the initially excited state within only similar to 200 fs in contrast to theoretically predicted picosecond population trapping behind a reaction barrier. Photoinduced charge transfer dynamics between transition metal complexes and semiconductor nanostructures are of central importance for many emerging energy and climate relevant technologies. Numerous demonstrations of photovoltaic and photocatalytic activity have been performed based on the combination of strong light absorption in dye molecules with charge separation and transport in adjacent semiconductor nanostructures. However, a fundamental understanding of the enabling and limiting dynamics on critical atomic length- and time scales is often still lacking. Femtosecond time-resolved X-ray photoelectron spectroscopy is employed to gain a better understanding of a short-lived intermediate that may be linked to the unexpectedly limited performance of ZnO based dye-sensitized solar cells by delaying the generation of free charge carriers. The transient spectra strongly suggest that photoexcited dye molecules attached to ZnO nanocrystals inject their charges into the substrate within less than 1 ps but the electrons are then temporarily trapped at the surface of the semiconductor in direct vicinity of the injecting molecules. The experiments are extended to monitor the electronic response of the semiconductor substrate to the collective injection from a monolayer of dye molecules and the subsequent electron-ion recombination dynamics. The results indicate some qualitative similarities but quantitative differences between the recombination dynamics at molecule-semiconductor interfaces and previously studied bulk-surface electron-hole recombination dynamics in photoexcited semiconductors.}, language = {en} } @article{MayerMatthaeiHeueretal.2019, author = {Mayer, Dennis and Matthaei, Christian T. and Heuer, Axel and G{\"u}hr, Markus}, title = {Kagome-fiber prism compressor combination for Yb}, series = {Journal of optics}, volume = {21}, journal = {Journal of optics}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2040-8978}, doi = {10.1088/2040-8986/aafdf6}, pages = {6}, year = {2019}, abstract = {Spectral broadening in hollow-core fibers is an important tool for pulse compression of low-peak power laser pulses, especially for Yb-based lasers. Here, we present a pulse compression scheme to reduce the pulse duration of a commercial Yb:KGW laser operating at 100 kHz repetition rate and 40 mu J pulse energy from 390 to 38 fs. The spectral broadening is accomplished using a krypton-filled Kagome-type fiber. We report broadened spectra for variable Kr-pressures and input powers. At optimal settings of 8 bar Kr-pressure and 3.3 W input power, the bandwidth of the pulse at the -10 dB level increased from 9.5 to 85 nm corresponding to a Fourier limit of 26 fs. A simple SF10 prism compressor is used to reduce the accumulated chirp and shortens the fiber output from about 500 to 38 fs. In addition to the spectral broadening, a pressure dependent change of the polarization is observed.}, language = {en} } @article{YangZhuWolfetal.2018, author = {Yang, Jie and Zhu, Xiaolei and Wolf, Thomas J. A. and Li, Zheng and Nunes, Jo{\~a}o Pedro Figueira and Coffee, Ryan and Cryan, James P. and G{\"u}hr, Markus and Hegazy, Kareem and Heinz, Tony F. and Jobe, Keith and Li, Renkai and Shen, Xiaozhe and Veccione, Theodore and Weathersby, Stephen and Wilkin, Kyle J. and Yoneda, Charles and Zheng, Qiang and Martinez, Todd J. and Centurion, Martin and Wang, Xijie}, title = {Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction}, series = {Science}, volume = {361}, journal = {Science}, number = {6397}, publisher = {American Assoc. for the Advancement of Science}, address = {Washington}, issn = {0036-8075}, doi = {10.1126/science.aat0049}, pages = {64 -- 67}, year = {2018}, abstract = {Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF3I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.}, language = {en} } @article{XiongFangOsipovetal.2018, author = {Xiong, Hui and Fang, Li and Osipov, Timur and Kling, Nora G. and Wolf, Thomas J. A. and Sistrunk, Emily and Obaid, Razib and G{\"u}hr, Markus and Berrah, Nora}, title = {Fragmentation of endohedral fullerene Ho3N@C-80 in an intense femtosecond near-infrared laser field}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {97}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9926}, doi = {10.1103/PhysRevA.97.023419}, pages = {7}, year = {2018}, abstract = {The fragmentation of gas phase endohedral fullerene, Ho3N@C-80, was investigated using femtosecond near-infrared laser pulses with an ion velocity map imaging spectrometer. We observed that Ho+ abundance associated with carbon cage opening dominates at an intensity of 1.1 x 10(14) W/cm(2). As the intensity increases, the Ho+ yield associated with multifragmentation of the carbon cage exceeds the prominence of Ho+ associated with the gentler carbon cage opening. Moreover, the power law dependence of Ho+ on laser intensity indicates that the transition of the most likely fragmentation mechanisms occurs around 2.0 x 10(14) W/cm(2).}, language = {en} } @misc{MayerLeverPicconietal.2022, author = {Mayer, Dennis and Lever, Fabiano and Picconi, David and Metje, Jan and Ališauskas, Skirmantas and Calegari, Francesca and D{\"u}sterer, Stefan and Ehlert, Christopher and Feifel, Raimund and Niebuhr, Mario and Manschwetus, Bastian and Kuhlmann, Marion and Mazza, Tommaso and Robinson, Matthew Scott and Squibb, Richard James and Trabattoni, Andrea and Wallner, M{\aa}ns and Saalfrank, Peter and Wolf, Thomas J. A. and G{\"u}hr, Markus}, title = {Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1301}, issn = {1866-8372}, doi = {10.25932/publishup-57744}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-577442}, pages = {9}, year = {2022}, abstract = {The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220-250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.}, language = {en} } @article{MayerLeverPicconietal.2022, author = {Mayer, Dennis and Lever, Fabiano and Picconi, David and Metje, Jan and Ališauskas, Skirmantas and Calegari, Francesca and D{\"u}sterer, Stefan and Ehlert, Christopher and Feifel, Raimund and Niebuhr, Mario and Manschwetus, Bastian and Kuhlmann, Marion and Mazza, Tommaso and Robinson, Matthew Scott and Squibb, Richard J. and Trabattoni, Andrea and Wallner, M{\aa}ns and Saalfrank, Peter and Wolf, Thomas J. A. and G{\"u}hr, Markus}, title = {Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy}, series = {Nature communications}, volume = {13}, journal = {Nature communications}, number = {1}, publisher = {Nature Research}, address = {Berlin}, issn = {2041-1723}, doi = {10.1038/s41467-021-27908-y}, pages = {9}, year = {2022}, abstract = {Imaging the charge flow in photoexcited molecules would provide key information on photophysical and photochemical processes. Here the authors demonstrate tracking in real time after photoexcitation the change in charge density at a specific site of 2-thiouracil using time-resolved X-ray photoelectron spectroscopy. The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220-250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.}, language = {en} } @article{MayerLeverPicconietal.2022, author = {Mayer, Dennis and Lever, Fabiano and Picconi, David and Metje, Jan and Ališauskas, Skirmantas and Calegari, Francesca and D{\"u}sterer, Stefan and Ehlert, Christopher and Feifel, Raimund and Niebuhr, Mario and Manschwetus, Bastian and Kuhlmann, Marion and Mazza, Tommaso and Robinson, Matthew Scott and Squibb, Richard James and Trabattoni, Andrea and Wallner, M{\aa}ns and Saalfrank, Peter and Wolf, Thomas J. A. and G{\"u}hr, Markus}, title = {Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy}, series = {Nature Communications}, volume = {13}, journal = {Nature Communications}, publisher = {Springer Nature}, address = {Berlin}, issn = {2041-1723}, doi = {10.1038/s41467-021-27908-y}, pages = {9}, year = {2022}, abstract = {The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220-250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.}, language = {en} } @article{YangGuehrVecchioneetal.2016, author = {Yang, Jie and G{\"u}hr, Markus and Vecchione, Theodore and Robinson, Matthew Scott and Li, Renkai and Hartmann, Nick and Shen, Xiaozhe and Coffee, Ryan and Corbett, Jeff and Fry, Alan and Gaffney, Kelly and Gorkhover, Tais and Hast, Carsten and Jobe, Keith and Makasyuk, Igor and Reid, Alexander and Robinson, Joseph and Vetter, Sharon and Wang, Fenglin and Weathersby, Stephen and Yoneda, Charles and Wang, Xijie and Centurion, Martin}, title = {Femtosecond gas phase electron diffraction with MeV electrons}, series = {Faraday discussions}, volume = {194}, journal = {Faraday discussions}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1359-6640}, doi = {10.1039/c6fd00071a}, pages = {563 -- 581}, year = {2016}, abstract = {We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.}, language = {en} } @article{MayerPicconiRobinsonetal.2022, author = {Mayer, Dennis and Picconi, David and Robinson, Matthew S. and G{\"u}hr, Markus}, title = {Experimental and theoretical gas-phase absorption spectra of thionated uracils}, series = {Chemical physics : a journal devoted to experimental and theoretical research involving problems of both a chemical and physical nature}, volume = {558}, journal = {Chemical physics : a journal devoted to experimental and theoretical research involving problems of both a chemical and physical nature}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0301-0104}, doi = {10.1016/j.chemphys.2022.111500}, pages = {9}, year = {2022}, abstract = {We present a comparative study of the gas-phase UV spectra of uracil and its thionated counterparts (2-thiouracil, 4-thiouracil and 2,4-dithiouracil), closely supported by time-dependent density functional theory calculations to assign the transitions observed. We systematically discuss pure gas-phase spectra for the (thio)uracils in the range of 200-400 nm (similar to 3.2-6.4 eV), and examine the spectra of all four species with a single theoretical approach. We note that specific vibrational modelling is needed to accurately determine the spectra across the examined wavelength range, and systematically model the transitions that appear at wavelengths shorter than 250 nm. Additionally, we find in the cases of 2-thiouracil and 2,4-dithiouracil, that the gas-phase spectra deviate significantly from some previously published solution-phase spectra, especially those collected in basic environments.}, language = {en} } @article{LeverRamelowGuehr2019, author = {Lever, Fabiano and Ramelow, Sven and G{\"u}hr, Markus}, title = {Effects of time-energy correlation strength in molecular entangled photon spectroscopy}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {100}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.053844}, pages = {6}, year = {2019}, abstract = {In this paper, we explore the time-energy domain quantum-classical transition comparing a classical pump-probe experiment on a diatomic molecule to its quantum enhanced counterpart, where the pump and probe pulses are substituted by the signal and idler beams of a spontaneous parametric down conversion (SPDC) source. Absorption of biphotons generated with SPDC exploits quantum time-energy entanglement to enhance the overall yield and selectivity of the process, when compared with a classical pump-probe setup, while maintaining femtosecond time resolution. We systematically study the effects of correlation strength on process efficiency and selectivity, comparing the results to classical pump-probe spectra. An excitation scheme to improve the yield based on spectral narrowing of biphotons is shown. The results indicate that the quantum improvements in yield are caused by a more efficient use of the total power available for the process.}, language = {en} } @article{WilkinParrishYangetal.2019, author = {Wilkin, Kyle J. and Parrish, Robert M. and Yang, Jie and Wolf, Thomas J. A. and Nunes, J. Pedro F. and G{\"u}hr, Markus and Li, Renkai and Shen, Xiaozhe and Zheng, Qiang and Wang, Xijie and Martinez, Todd J. and Centurion, Martin}, title = {Diffractive imaging of dissociation and ground-state dynamics in a complex molecule}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {100}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.023402}, pages = {10}, year = {2019}, abstract = {We have investigated the structural dynamics in photoexcited 1,2-diiodotetrafluoroethane molecules (C2F4I2) in the gas phase experimentally using ultrafast electron diffraction and theoretically using FOMO-CASCI excited-state dynamics simulations. The molecules are excited by an ultraviolet femtosecond laser pulse to a state characterized by a transition from the iodine 5p perpendicular to orbital to a mixed 5p parallel to sigma hole and CF2 center dot antibonding orbital, which results in the cleavage of one of the carbon-iodine bonds. We have observed, with sub-Angstrom resolution, the motion of the nuclear wave packet of the dissociating iodine atom followed by coherent vibrations in the electronic ground state of the C2F4I radical. The radical reaches a stable classical (nonbridged) structure in less than 200 fs.}, language = {en} } @article{YangGuehrVecchioneetal.2016, author = {Yang, Jie and G{\"u}hr, Markus and Vecchione, Theodore and Robinson, Matthew Scott and Li, Renkai and Hartmann, Nick and Shen, Xiaozhe and Coffee, Ryan and Corbett, Jeff and Fry, Alan and Gaffney, Kelly and Gorkhover, Tais and Hast, Carsten and Jobe, Keith and Makasyuk, Igor and Reid, Alexander and Robinson, Joseph and Vetter, Sharon and Wang, Fenglin and Weathersby, Stephen and Yoneda, Charles and Centurion, Martin and Wang, Xijie}, title = {Diffractive imaging of a rotational wavepacket in nitrogen molecules with femtosecond megaelectronvolt electron pulses}, series = {Nature Communications}, volume = {7}, journal = {Nature Communications}, publisher = {Nature Publ. Group}, address = {London}, issn = {2041-1723}, doi = {10.1038/ncomms11232}, pages = {9}, year = {2016}, abstract = {Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angstrom spatial precision is one of the critical challenges in the chemical sciences, as the nuclear geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. Here we report a gas-phase electron diffraction experiment using megaelectronvolt (MeV) electrons, where we captured the rotational wavepacket dynamics of nonadiabatically laser-aligned nitrogen molecules. We achieved a combination of 100 fs root-mean-squared temporal resolution and sub-Angstrom (0.76 angstrom) spatial resolution that makes it possible to resolve the position of the nuclei within the molecule. In addition, the diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in 300 fs. Our results demonstrate a significant and promising step towards making atomically resolved movies of molecular reactions.}, language = {en} } @article{MayerLeverGuehr2022, author = {Mayer, Dennis and Lever, Fabiano and G{\"u}hr, Markus}, title = {Data analysis procedures for time-resolved x-ray photoelectron spectroscopy at a SASE free-electron-laser}, series = {Journal of physics : B, Atomic, molecular and optical physics}, volume = {55}, journal = {Journal of physics : B, Atomic, molecular and optical physics}, number = {5}, publisher = {IOP Publ.}, address = {Bristol}, issn = {0953-4075}, doi = {10.1088/1361-6455/ac3c91}, pages = {9}, year = {2022}, abstract = {The random nature of self-amplified spontaneous emission (SASE) is a well-known challenge for x-ray core level spectroscopy at SASE free-electron lasers (FELs). Especially in time-resolved experiments that require a combination of good temporal and spectral resolution the jitter and drifts in the spectral characteristics, relative arrival time as well as power fluctuations can smear out spectral-temporal features. We present a combination of methods for the analysis of time-resolved photoelectron spectra based on power and time corrections as well as self-referencing of a strong photoelectron line. Based on sulfur 2p photoelectron spectra of 2-thiouracil taken at the SASE FEL FLASH2, we show that it is possible to correct for some of the photon energy drift and jitter even when reliable shot-to-shot photon energy data is not available. The quality of pump-probe difference spectra improves as random jumps in energy between delay points reduce significantly. The data analysis allows to identify coherent oscillations of 1 eV shift on the mean photoelectron line of 4 eV width with an error of less than 0.1 eV.}, language = {en} } @misc{LeverMayerMetjeetal.2021, author = {Lever, Fabiano and Mayer, Dennis and Metje, Jan and Alisauskas, Skirmantas and Calegari, Francesca and D{\"u}sterer, Stefan and Feifel, Raimund and Niebuhr, Mario and Manschwetus, Bastian and Kuhlmann, Marion and Mazza, Tommaso and Robinson, Matthew Scott and Squibb, Richard J. and Trabattoni, Andrea and Wallner, M{\aa}ns and Wolf, Thomas J. A. and G{\"u}hr, Markus}, title = {Core-level spectroscopy of 2-thiouracil at the sulfur L1 and L2,3 edges utilizing a SASE free-electron-laser}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {21}, issn = {1866-8372}, doi = {10.25932/publishup-52409}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-524091}, pages = {13}, year = {2021}, abstract = {In this paper, we report X-ray absorption and core-level electron spectra of the nucleobase derivative 2-thiouracil at the sulfur L1- and L2,3-edges. We used soft X-rays from the free-electron laser FLASH2 for the excitation of isolated molecules and dispersed the outgoing electrons with a magnetic bottle spectrometer. We identified photoelectrons from the 2p core orbital, accompanied by an electron correlation satellite, as well as resonant and non-resonant Coster-Kronig and Auger-Meitner emission at the L1- and L2,3-edges, respectively. We used the electron yield to construct X-ray absorption spectra at the two edges. The experimental data obtained are put in the context of the literature currently available on sulfur core-level and 2-thiouracil spectroscopy.}, language = {en} } @article{LeverMayerMetjeetal.2021, author = {Lever, Fabiano and Mayer, Dennis and Metje, Jan and Alisauskas, Skirmantas and Calegari, Francesca and D{\"u}sterer, Stefan and Feifel, Raimund and Niebuhr, Mario and Manschwetus, Bastian and Kuhlmann, Marion and Mazza, Tommaso and Robinson, Matthew Scott and Squibb, Richard J. and Trabattoni, Andrea and Wallner, M{\aa}ns and Wolf, Thomas J. A. and G{\"u}hr, Markus}, title = {Core-level spectroscopy of 2-thiouracil at the sulfur L1 and L2,3 edges utilizing a SASE free-electron-laser}, series = {Molecules}, volume = {26}, journal = {Molecules}, number = {21}, publisher = {MDPI}, address = {Basel}, issn = {1420-3049}, pages = {11}, year = {2021}, abstract = {In this paper, we report X-ray absorption and core-level electron spectra of the nucleobase derivative 2-thiouracil at the sulfur L1- and L2,3-edges. We used soft X-rays from the free-electron laser FLASH2 for the excitation of isolated molecules and dispersed the outgoing electrons with a magnetic bottle spectrometer. We identified photoelectrons from the 2p core orbital, accompanied by an electron correlation satellite, as well as resonant and non-resonant Coster-Kronig and Auger-Meitner emission at the L1- and L2,3-edges, respectively. We used the electron yield to construct X-ray absorption spectra at the two edges. The experimental data obtained are put in the context of the literature currently available on sulfur core-level and 2-thiouracil spectroscopy.}, language = {en} } @article{EhlertGuehrSaalfrank2018, author = {Ehlert, Christopher and G{\"u}hr, Markus and Saalfrank, Peter}, title = {An efficient first principles method for molecular pump-probe NEXAFS spectra}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {149}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {14}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.5050488}, pages = {13}, year = {2018}, abstract = {Pump-probe near edge X-ray absorption fine structure (PP-NEXAFS) spectra of molecules offer insight into valence-excited states, even if optically dark. In PP-NEXAFS spectroscopy, the molecule is "pumped" by UV or visible light enforcing a valence excitation, followed by an X-ray "probe" exciting core electrons into (now) partially empty valence orbitals. Calculations of PP-NEXAFS have so far been done by costly, correlated wavefunction methods which are not easily applicable to medium-sized or large molecules. Here we propose an efficient, first principles method based on density functional theory in combination with the transition potential and Delta SCF methodology (TP-DFT/Delta SCF) to compute molecular ground state and PP-NEXAFS spectra. We apply the method to n ->pi* pump/O-K-edge NEXAFS probe spectroscopy of thymine (for which both experimental and other theoretical data exist) and to n -> pi* or pi -> pi* pump/N-K-edge NEXAFS probe spectroscopies of trans-and cis-azobenzene. Published by AIP Publishing.}, language = {en} } @article{BattistoniDuerrGuehretal.2018, author = {Battistoni, A. and D{\"u}rr, H. A. and G{\"u}hr, Markus and Wolf, Thomas J. A.}, title = {A tilted pulse-front setup for femtosecond transient grating spectroscopy in highly non-collinear geometries}, series = {Journal of optics}, volume = {20}, journal = {Journal of optics}, number = {9}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2040-8978}, doi = {10.1088/2040-8986/aad60a}, pages = {5}, year = {2018}, abstract = {We demonstrate a tilted pulse-front transient grating (TG) technique that allows to optimally utilize time resolution as well as TG line density while probing under grazing incidence as typically done in extreme ultraviolet (EUV) or soft x-ray (SXR) experiments. Our optical setup adapts the pulse front tilt of the two pulses that create the TG to the grazing incident pulse. We demonstrate the technique using all 800 nm femtosecond laser pulses for TG generation on a vanadium dioxide film. We probe that grating via diffraction of a third 800 nm pulse. The time resolution of 90 fs is an improvement by a factor of 30 compared to our previous experiments on the same system. The scheme paves the way for EUV and SXR probing of optically induced TGs on any material.}, language = {en} } @article{MyhreWolfChengetal.2018, author = {Myhre, Rolf H. and Wolf, Thomas J. A. and Cheng, Lan and Nandi, Saikat and Coriani, Sonia and G{\"u}hr, Markus and Koch, Henrik}, title = {A theoretical and experimental benchmark study of core-excited states in nitrogen}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {148}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {6}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.5011148}, pages = {7}, year = {2018}, abstract = {The high resolution near edge X-ray absorption fine structure spectrum of nitrogen displays the vibrational structure of the core-excited states. This makes nitrogen well suited for assessing the accuracy of different electronic structure methods for core excitations. We report high resolution experimental measurements performed at the SOLEIL synchrotron facility. These are compared with theoretical spectra calculated using coupled cluster theory and algebraic diagrammatic construction theory. The coupled cluster singles and doubles with perturbative triples model known as CC3 is shown to accurately reproduce the experimental excitation energies as well as the spacing of the vibrational transitions. The computational results are also shown to be systematically improved within the coupled cluster hierarchy, with the coupled cluster singles, doubles, triples, and quadruples method faithfully reproducing the experimental vibrational structure. Published by AIP Publishing.}, language = {en} }