@misc{SchickEckertPontiusetal.2016, author = {Schick, Daniel and Eckert, Sebastian and Pontius, Niko and Mitzner, Rolf and F{\"o}hlisch, Alexander and Holldack, Karsten and Sorgenfrei, Florian}, title = {Versatile soft X-ray-optical cross-correlator for ultrafast applications}, 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 = {1331}, issn = {1866-8372}, doi = {10.25932/publishup-43696}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436962}, pages = {054304-1 -- 054304-8}, year = {2016}, abstract = {We present an X-ray-optical cross-correlator for the soft (> 150 eV) up to the hard X-ray regime based on a molybdenum-silicon superlattice. The cross-correlation is done by probing intensity and position changes of superlattice Bragg peaks caused by photoexcitation of coherent phonons. This approach is applicable for a wide range of X-ray photon energies as well as for a broad range of excitation wavelengths and requires no external fields or changes of temperature. Moreover, the cross-correlator can be employed on a 10 ps or 100 fs time scale featuring up to 50\% total X-ray reflectivity and transient signal changes of more than 20\%. (C) 2016 Author(s).}, language = {en} } @misc{TomovPenaRoqueetal.2016, author = {Tomov, Petar and Pena, Rodrigo F. O. and Roque, Antonio C. and Zaks, Michael A.}, title = {Mechanisms of self-sustained oscillatory states in hierarchical modular networks with mixtures of electrophysiological cell types}, series = {Frontiers in computational neuroscience}, journal = {Frontiers in computational neuroscience}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407724}, pages = {17}, year = {2016}, abstract = {In a network with a mixture of different electrophysiological types of neurons linked by excitatory and inhibitory connections, temporal evolution leads through repeated epochs of intensive global activity separated by intervals with low activity level. This behavior mimics "up" and "down" states, experimentally observed in cortical tissues in absence of external stimuli. We interpret global dynamical features in terms of individual dynamics of the neurons. In particular, we observe that the crucial role both in interruption and in resumption of global activity is played by distributions of the membrane recovery variable within the network. We also demonstrate that the behavior of neurons is more influenced by their presynaptic environment in the network than by their formal types, assigned in accordance with their response to constant current.}, language = {en} } @misc{NishikawaMizunoNiemiecetal.2016, author = {Nishikawa, Ken-Ichi and Mizuno, Yosuke and Niemiec, Jacek and Kobzar, Oleh and Pohl, Martin and G{\´o}mez, Jose L. and Duţan, Ioana and Pe'er, Asaf and Frederiksen, Jacob Trier and Nordlund, {\AA}ke and Meli, Athina and Sol, Helene and Hardee, Philip E. and Hartmann, Dieter H.}, title = {Microscopic processes in global relativistic jets containing helical magnetic fields}, series = {Galaxies}, journal = {Galaxies}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407604}, pages = {9}, year = {2016}, abstract = {In the study of relativistic jets one of the key open questions is their interaction with the environment on the microscopic level. Here, we study the initial evolution of both electron-proton (e(-)-p(+)) and electron-positron (e(+/-)) relativistic jets containing helical magnetic fields, focusing on their interaction with an ambient plasma. We have performed simulations of "global" jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities such as the Weibel instability, the kinetic Kelvin-Helmholtz instability (kKHI) and the Mushroom instability (MI). In our initial simulation study these kinetic instabilities are suppressed and new types of instabilities can grow. In the e(-)-p(+) jet simulation a recollimation-like instability occurs and jet electrons are strongly perturbed. In the e(+/-) jet simulation a recollimation-like instability occurs at early times followed by a kinetic instability and the general structure is similar to a simulation without helical magnetic field. Simulations using much larger systems are required in order to thoroughly follow the evolution of global jets containing helical magnetic fields.}, language = {en} } @phdthesis{Bendre2016, author = {Bendre, Abhijit B.}, title = {Growth and saturation of dynamo in spiral galaxies via direct simulations}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407517}, school = {Universit{\"a}t Potsdam}, pages = {xviii, 133}, year = {2016}, abstract = {We do magnetohydrodynamic (MHD) simulations of local box models of turbulent Interstellar Medium (ISM) and analyse the process of amplification and saturation of mean magnetic fields with methods of mean field dynamo theory. It is shown that the process of saturation of mean fields can be partially described by the prolonged diffusion time scales in presence of the dynamically significant magnetic fields. However, the outward wind also plays an essential role in the saturation in higher SN rate case. Algebraic expressions for the back reaction of the magnetic field onto the turbulent transport coefficients are derived, which allow a complete description of the nonlinear dynamo. We also present the effects of dynamically significant mean fields on the ISM configuration and pressure distribution. We further add the cosmic ray component in the simulations and investigate the kinematic growth of mean fields with a dynamo perspective.}, language = {en} } @phdthesis{Brauer2016, author = {Brauer, Doroth{\´e}e}, title = {Chemo-kinematic constraints on Milky Way models from the spectroscopic surveys SEGUE \& RAVE}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-403968}, school = {Universit{\"a}t Potsdam}, pages = {vii, 197}, year = {2016}, abstract = {The Milky Way is only one out of billions of galaxies in the universe. However, it is a special galaxy because it allows to explore the main mechanisms involved in its evolution and formation history by unpicking the system star-by-star. Especially, the chemical fingerprints of its stars provide clues and evidence of past events in the Galaxy's lifetime. These information help not only to decipher the current structure and building blocks of the Milky Way, but to learn more about the general formation process of galaxies. In the past decade a multitude of stellar spectroscopic Galactic surveys have scanned millions of stars far beyond the rim of the solar neighbourhood. The obtained spectroscopic information provide unprecedented insights to the chemo-dynamics of the Milky Way. In addition analytic models and numerical simulations of the Milky Way provide necessary descriptions and predictions suited for comparison with observations in order to decode the physical properties that underlie the complex system of the Galaxy. In the thesis various approaches are taken to connect modern theoretical modelling of galaxy formation and evolution with observations from Galactic stellar surveys. With its focus on the chemo-kinematics of the Galactic disk this work aims to determine new observational constraints on the formation of the Milky Way providing also proper comparisons with two different models. These are the population synthesis model TRILEGAL based on analytical distribution functions, which aims to simulate the number and distribution of stars in the Milky Way and its different components, and a hybrid model (MCM) that combines an N-body simulation of a Milky Way like galaxy in the cosmological framework with a semi-analytic chemical evolution model for the Milky Way. The major observational data sets in use come from two surveys, namely the "Radial Velocity Experiment" (RAVE) and the "Sloan Extension for Galactic Understanding and Exploration" (SEGUE). In the first approach the chemo-kinematic properties of the thin and thick disk of the Galaxy as traced by a selection of about 20000 SEGUE G-dwarf stars are directly compared to the predictions by the MCM model. As a necessary condition for this, SEGUE's selection function and its survey volume are evaluated in detail to correct the spectroscopic observations for their survey specific selection biases. Also, based on a Bayesian method spectro-photometric distances with uncertainties below 15\% are computed for the selection of SEGUE G-dwarfs that are studied up to a distance of 3 kpc from the Sun. For the second approach two synthetic versions of the SEGUE survey are generated based on the above models. The obtained synthetic stellar catalogues are then used to create mock samples best resembling the compiled sample of observed SEGUE G-dwarfs. Generally, mock samples are not only ideal to compare predictions from various models. They also allow validation of the models' quality and improvement as with this work could be especially achieved for TRILEGAL. While TRILEGAL reproduces the statistical properties of the thin and thick disk as seen in the observations, the MCM model has shown to be more suitable in reproducing many chemo-kinematic correlations as revealed by the SEGUE stars. However, evidence has been found that the MCM model may be missing a stellar component with the properties of the thick disk that the observations clearly show. While the SEGUE stars do indicate a thin-thick dichotomy of the stellar Galactic disk in agreement with other spectroscopic stellar studies, no sign for a distinct metal-poor disk is seen in the MCM model. Usually stellar spectroscopic surveys are limited to a certain volume around the Sun covering different regions of the Galaxy's disk. This often prevents to obtain a global view on the chemo-dynamics of the Galactic disk. Hence, a suitable combination of stellar samples from independent surveys is not only useful for the verification of results but it also helps to complete the picture of the Milky Way. Therefore, the thesis closes with a comparison of the SEGUE G-dwarfs and a sample of RAVE giants. The comparison reveals that the chemo-kinematic relations agree in disk regions where the samples of both surveys show a similar number of stars. For those parts of the survey volumes where one of the surveys lacks statistics they beautifully complement each other. This demonstrates that the comparison of theoretical models on the one side, and the combined observational data gathered by multiple surveys on the other side, are key ingredients to understand and disentangle the structure and formation history of the Milky Way.}, language = {en} } @phdthesis{Ata2016, author = {Ata, Metin}, title = {Phase-space reconstructions of cosmic velocities and the cosmic web}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-403565}, school = {Universit{\"a}t Potsdam}, pages = {xi, 155}, year = {2016}, abstract = {In the current paradigm of cosmology, the formation of large-scale structures is mainly driven by non-radiating dark matter, making up the dominant part of the matter budget of the Universe. Cosmological observations however, rely on the detection of luminous galaxies, which are biased tracers of the underlying dark matter. In this thesis I present cosmological reconstructions of both, the dark matter density field that forms the cosmic web, and cosmic velocities, for which both aspects of my work are delved into, the theoretical formalism and the results of its applications to cosmological simulations and also to a galaxy redshift survey.The foundation of our method is relying on a statistical approach, in which a given galaxy catalogue is interpreted as a biased realization of the underlying dark matter density field. The inference is computationally performed on a mesh grid by sampling from a probability density function, which describes the joint posterior distribution of matter density and the three dimensional velocity field. The statistical background of our method is described in Chapter "Implementation of argo", where the introduction in sampling methods is given, paying special attention to Markov Chain Monte-Carlo techniques. In Chapter "Phase-Space Reconstructions with N-body Simulations", I introduce and implement a novel biasing scheme to relate the galaxy number density to the underlying dark matter, which I decompose into a deterministic part, described by a non-linear and scale-dependent analytic expression, and a stochastic part, by presenting a negative binomial (NB) likelihood function that models deviations from Poissonity. Both bias components had already been studied theoretically, but were so far never tested in a reconstruction algorithm. I test these new contributions againstN-body simulations to quantify improvements and show that, compared to state-of-the-art methods, the stochastic bias is inevitable at wave numbers of k≥0.15h Mpc^-1 in the power spectrum in order to obtain unbiased results from the reconstructions. In the second part of Chapter "Phase-Space Reconstructions with N-body Simulations" I describe and validate our approach to infer the three dimensional cosmic velocity field jointly with the dark matter density. I use linear perturbation theory for the large-scale bulk flows and a dispersion term to model virialized galaxy motions, showing that our method is accurately recovering the real-space positions of the redshift-space distorted galaxies. I analyze the results with the isotropic and also the two-dimensional power spectrum.Finally, in Chapter "Phase-space Reconstructions with Galaxy Redshift Surveys", I show how I combine all findings and results and apply the method to the CMASS (for Constant (stellar) Mass) galaxy catalogue of the Baryon Oscillation Spectroscopic Survey (BOSS). I describe how our method is accounting for the observational selection effects inside our reconstruction algorithm. Also, I demonstrate that the renormalization of the prior distribution function is mandatory to account for higher order contributions in the structure formation model, and finally a redshift-dependent bias factor is theoretically motivated and implemented into our method. The various refinements yield unbiased results of the dark matter until scales of k≤0.2 h Mpc^-1in the power spectrum and isotropize the galaxy catalogue down to distances of r∼20h^-1 Mpc in the correlation function. We further test the results of our cosmic velocity field reconstruction by comparing them to a synthetic mock galaxy catalogue, finding a strong correlation between the mock and the reconstructed velocities. The applications of both, the density field without redshift-space distortions, and the velocity reconstructions, are very broad and can be used for improved analyses of the baryonic acoustic oscillations, environmental studies of the cosmic web, the kinematic Sunyaev-Zel'dovic or integrated Sachs-Wolfe effect.}, language = {en} } @phdthesis{Schulz2016, author = {Schulz, Alexander}, title = {Untersuchung der Wechselwirkung synoptisch-skaliger mit orographisch bedingten Prozessen in der arktischen Grenzschicht {\"u}ber Spitzbergen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400058}, school = {Universit{\"a}t Potsdam}, pages = {vi, 194}, year = {2016}, abstract = {In der vorliegenden Arbeit wird die planetare Grenzschicht in Ny-{\AA}lesund, Spitzbergen, sowohl bez{\"u}glich kleinskaliger („mikrometeorologischer") Effekte als auch in ihrer Kopplung mit der Synoptik untersucht. Dazu werden verschiedene Beobachtungsdaten aus der S{\"a}ule und in Bodenn{\"a}he zusammengezogen und bewertet. Die so gewonnenen Datens{\"a}tze werden dann zur Validierung eines nicht-hydrostatischen, regionalen Klimamodells genutzt. Weiterhin werden orographisch bedingte Einfl{\"u}sse, die Untergrundbeschaffenheit und die lokale Heterogenit{\"a}t der Unterlage untersucht. Hierzu werden meteorologische Gr{\"o}ßen, wie die Variabilit{\"a}t der Temperatur und insbesondere die j{\"a}hrliche Windverteilung in Bodenn{\"a}he untersucht und es erfolgt ein Vergleich von in-situ gemessenen turbulenten Fl{\"u}ssen von den Eddy-Kovarianz-Messkomplexen bei Ny-{\AA}lesund und im Bayelva-Tal unter demselben Aspekt. Es zeigt sich, dass der Eddy-Kovarianz-Messkomplex im Bayelva-Tal sehr stark durch eine orographisch bedingte Kanalisierung der Str{\"o}mung beeinflusst ist und sich nicht f{\"u}r Vergleiche mit regionalen Klimamodellen mit horizontalen Aufl{\"o}sungen von <1km eignet. Die hohe Bodenfeuchte im Bayelva-Tal f{\"u}hrt zudem zu einem deutlich kleineren Bowen-Verh{\"a}ltnis, als es f{\"u}r diese Region zu erwarten ist. Der Eddy-Kovarianz-Messkomplex bei Ny-{\AA}lesund erweist sich hingegen als geeigneter f{\"u}r solche Modellvergleiche, aufgrund der typischen, k{\"u}stennahen Windverteilung und des repr{\"a}sentativen Footprints. Letzteres wird durch die Bestimmung der Footprint-Klimatologie des Jahres 2013 mit einem aktuellen Footprint-Modell erarbeitet. Weiterhin wird die Auswirkung von (Anti-) Zyklonen {\"u}ber den Archipel auf die zeitliche Variabilit{\"a}t der lokalen Grenzschichteigenschaften untersucht und bewertet. Dazu wird ein Zyklonen-Detektions-Algorithmus auf ERA-Interim-Reanalysedatens{\"a}tze angewendet, wodurch die H{\"a}ufigkeit von nahezu ideal konzentrischen Hoch- und die Tiefdruckgebieten f{\"u}r drei Jahre bestimmt wird. Aus dieser Verteilung werden insgesamt drei interessante Zeitr{\"a}ume zu verschiedenen Jahreszeiten ausgew{\"a}hlt und im Rahmen von Prozessstudien die lokalen bodennahen meteorologischen Messungen, der turbulente Austausch an der Oberfl{\"a}che und die Grenzschichtdynamik in der S{\"a}ule untersucht. Die zeitliche Variabilit{\"a}t der dynamischen Grenzschichtstabilit{\"a}t in der S{\"a}ule wird anhand von zeitlich hoch aufgel{\"o}sten vertikalen Profilen der Bulk-Richardson-Zahl aus Kompositprofilen aus Fernerkundungsinstrumenten (Radiometer, Wind-LIDAR) sowie Mastdaten (BSRN-Mast) untersucht und die Grenzschichth{\"o}he ermittelt. Aus diesen Analysen ergibt sich eine deutliche Abh{\"a}ngigkeit der thermischen Stabilit{\"a}t beim Durchzug von Fronten, eine damit einhergehende erhebliche Abh{\"a}ngigkeit der Grenzschichtdynamik und der Grenzschichth{\"o}he sowie des turbulenten Austauschs von der zeitlichen Variabilit{\"a}t der Windgeschwindigkeit in der S{\"a}ule. Auf Grundlage der Standortanalysen und Prozessstudien erfolgt ein Vergleich der bodennahen Messungen und den Beobachtungen aus der S{\"a}ule, sowohl von den genannten Fernerkundungsinstrumenten als auch von In-situ-Messungen (Radiosonden) f{\"u}r den Zeitraum einer Radiosondierungskampagne mit dem nicht-hydrostatischen, regionalen Klimamodel WRF (ARW). Auf Grundlage der Fragestellung, inwieweit aktuelle Schemata die Grenzschichtcharakteristika in orographisch stark gegliedertem Gel{\"a}nde in der Arktis reproduzieren k{\"o}nnen, werden zwei Grenzschichtparametrisierungsschemata mit verschiedenen Ordnungen der Schließung validiert. Hierzu wird die zeitliche Variabilit{\"a}t der Temperatur, der Feuchte und des Windfeldes in der S{\"a}ule bis 2000m in den Simulationen mit den Beobachtungsdaten vergleichen. Es wird gezeigt, dass durch Modifikation der Initialwertfelder eine sehr gute {\"U}bereinstimmung zwischen den Simulationen und den Beobachtungen bereits bei einer horizontalen Aufl{\"o}sung von 1km erreicht werden kann und die Wahl des Grenzschichtschemas nur untergeordneten Einfluss hat. Hieraus werden Ans{\"a}tze der Weiterentwicklung der Parametrisierungen, aber auch Empfehlungen bez{\"u}glich der Initialwertfelder, wie der Landmaske und der Orographie, vorgeschlagen.}, language = {de} } @phdthesis{Breitling2016, author = {Breitling, Frank}, title = {Propagation of energetic electrons in the solar corona observed with LOFAR}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-396893}, school = {Universit{\"a}t Potsdam}, pages = {xiii, 101}, year = {2016}, abstract = {This work reports about new high-resolution imaging and spectroscopic observations of solar type III radio bursts at low radio frequencies in the range from 30 to 80 MHz. Solar type III radio bursts are understood as result of the beam-plasma interaction of electron beams in the corona. The Sun provides a unique opportunity to study these plasma processes of an active star. Its activity appears in eruptive events like flares, coronal mass ejections and radio bursts which are all accompanied by enhanced radio emission. Therefore solar radio emission carries important information about plasma processes associated with the Sun's activity. Moreover, the Sun's atmosphere is a unique plasma laboratory with plasma processes under conditions not found in terrestrial laboratories. Because of the Sun's proximity to Earth, it can be studied in greater detail than any other star but new knowledge about the Sun can be transfer to them. This "solar stellar connection" is important for the understanding of processes on other stars. The novel radio interferometer LOFAR provides imaging and spectroscopic capabilities to study these processes at low frequencies. Here it was used for solar observations. LOFAR, the characteristics of its solar data and the processing and analysis of the latter with the Solar Imaging Pipeline and Solar Data Center are described. The Solar Imaging Pipeline is the central software that allows using LOFAR for solar observations. So its development was necessary for the analysis of solar LOFAR data and realized here. Moreover a new density model with heat conduction and Alfv{\´e}n waves was developed that provides the distance of radio bursts to the Sun from dynamic radio spectra. Its application to the dynamic spectrum of a type III burst observed on March 16, 2016 by LOFAR shows a nonuniform radial propagation velocity of the radio emission. The analysis of an imaging observation of type III bursts on June 23, 2012 resolves a burst as bright, compact region localized in the corona propagating in radial direction along magnetic field lines with an average velocity of 0.23c. A nonuniform propagation velocity is revealed. A new beam model is presented that explains the nonuniform motion of the radio source as a propagation effect of an electron ensemble with a spread velocity distribution and rules out a monoenergetic electron distribution. The coronal electron number density is derived in the region from 1.5 to 2.5 R☉ and fitted with the newly developed density model. It determines the plasma density for the interplanetary space between Sun and Earth. The values correspond to a 1.25- and 5-fold Newkirk model for harmonic and fundamental emission, respectively. In comparison to data from other radio instruments the LOFAR data shows a high sensitivity and resolution in space, time and frequency. The new results from LOFAR's high resolution imaging spectroscopy are consistent with current theories of solar type III radio bursts and demonstrate its capability to track fast moving radio sources in the corona. LOFAR solar data is found to be a valuable source for solar radio physics and opens a new window for studying plasma processes associated with highly energetic electrons in the solar corona.}, language = {en} } @phdthesis{Fournier2016, author = {Fournier, Yori}, title = {Dynamics of the rise of magnetic flux tubes in stellar interiors}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394533}, school = {Universit{\"a}t Potsdam}, pages = {xii, 98}, year = {2016}, abstract = {In sonnen{\"a}hnlichen Sternen erh{\"a}lt ein Dynamo-Mechanismus die Magnetfelder. Der Babcock-Leighton-Dynamo beruht auf einem solchen Mechanismus und erfordert insbesondere die Existenz von magnetischen Flussr{\"o}hren. Man nimmt an, dass magnetische Flussr{\"o}hren am Boden der Konvetionszone entstehen und durch Auftrieb bis zur Oberfl{\"a}che steigen. Es wird ein spezielles Dynamomodell vorgeschlagen, in dem der Verz{\"o}gerungseffekt durch das Aufsteigen der Flussr{\"o}hren ber{\"u}cksichtigt wird. Die vorliegende Dissertation besch{\"a}ftigt sich mit der Anwendbarkeit des Babcock-Leighton-Dynamos auf andere Sterne. Zu diesem Zweck versuchen wir, die Aufstiegszeiten von magnetischen Flussr{\"o}hren mit Hilfe von kompressiblen MHD-Simulationen in sp{\"a}rischen Kugelschalen mit Dichteschichtung zu bestimmen und einzugrenzen. Derartige Simulationen sind allerdings nur in einem unrealistischen Parameterbereich m{\"o}glich. Deshalb ist eine Skalierungsrelation n{\"o}tig, die die Ergebnisse auf realistische physikalische Regimes {\"u}bertr{\"a}gt. Wir erweitern fr{\"u}here Arbeiten zu Skalierungsrelationen in 2D und leiten ein allgemeines Skalierungsgesetz ab, das f{\"u}r 2D- und 3D-Flussr{\"o}hren g{\"u}ltig ist. In einem umfangreichen Satz von numerischen Simulationen zeigen wir, dass die abgeleitete Skalierungsrelation auch im vollst{\"a}ndig nichtlinearen Fall gilt. Wir haben damit ein Gesetz f{\"u}r die Aufstiegszeit von magnetischen Flussr{\"o}hren gefunden, dass in jedem sonnen{\"a}hnlichen Stern G{\"u}ltigkeit hat. Schließlich implementieren wir dieses Gesetz in einem Dynamomodell mit Verz{\"o}gerungsterm. Die Simulationen eines solchen verz{\"o}gerten Flussr{\"o}hren/Babcock-Leighton-Dynamos auf der Basis der Meanfield-Formulierung f{\"u}hrten auf ein neues Dynamo-Regime, das nur bei Anwesenheit der Verz{\"o}gerung existiert. Die erforderlichen Verz{\"o}gerungen sind von der Gr{\"o}{\"y}enordnung der Zyklusl{\"a}nge, die resultierenden Magnetfelder sind schw{\"a}cher als die {\"A}quipartitions-Feldst{\"a}rke. Dieses neue Regime zeigt, dass auch bei sehr langen Aufstiegszeiten der Flussr{\"o}hren/Babcock-Leighton-Dynamo noch nichtzerfallende L{\"o}sungen liefern und daher auf ein breites Spektrum von Sternen anwendbar sein kann.}, language = {en} } @misc{NiskanenKooserKoskeloetal.2016, author = {Niskanen, Johannes and Kooser, Kuno and Koskelo, Jaakko and K{\"a}{\"a}mbre, Tanel and Kunnus, Kristjan and Pietzsch, Annette and Quevedo, Wilson and Hakala, Mikko and F{\"o}hlisch, Alexander and Huotari, Simo and Kukk, Edwin}, title = {Density functional simulation of resonant inelastic X-ray scattering experiments in liquids: acetonitrile}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-395133}, pages = {7}, year = {2016}, abstract = {In this paper we report an experimental and computational study of liquid acetonitrile (H3C-C[triple bond, length as m-dash]N) by resonant inelastic X-ray scattering (RIXS) at the N K-edge. The experimental spectra exhibit clear signatures of the electronic structure of the valence states at the N site and incident-beam-polarization dependence is observed as well. Moreover, we find fine structure in the quasielastic line that is assigned to finite scattering duration and nuclear relaxation. We present a simple and light-to-evaluate model for the RIXS maps and analyze the experimental data using this model combined with ab initio molecular dynamics simulations. In addition to polarization-dependence and scattering-duration effects, we pinpoint the effects of different types of chemical bonding to the RIXS spectrum and conclude that the H2C-C[double bond, length as m-dash]NH isomer, suggested in the literature, does not exist in detectable quantities. We study solution effects on the scattering spectra with simulations in liquid and in vacuum. The presented model for RIXS proved to be light enough to allow phase-space-sampling and still accurate enough for identification of transition lines in physical chemistry research by RIXS.}, language = {en} }