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- ItemIR-MALDI Mass Spectrometry Imaging with Plasma Post-Ionization of Nonpolar Metabolites(Columbus, Ohio : American Chemical Society, 2022) Schneemann, Julian; Schäfer, Karl-Christian; Spengler, Bernhard; Heiles, SvenAmbient mass spectrometry imaging (MSI) methods come with the advantage of visualizing biomolecules from tissues with no or minimal sample preparation and operation under atmospheric-pressure conditions. Similar to all other MSI methodologies, however, ambient MSI modalities suffer from a pronounced bias toward either polar or nonpolar analytes due to the underlying desorption and ionization mechanisms of the ion source. In this study, we present the design, construction, testing, and application of an in-capillary dielectric barrier discharge (DBD) module for post-ionization of neutrals desorbed by an ambient infrared matrix-assisted laser desorption/ionization (IR-MALDI) MSI source. We demonstrate that the DBD device enhances signal intensities of nonpolar compounds by up to 104 compared to IR-MALDI without affecting transmission of IR-MALDI ions. This allows performing MSI experiments of mouse tissue and Danaus plexippus caterpillar tissue sections, visualizing the distribution of sterols, fatty acids, monoglycerides, and diglycerides that are not detected in IR-MALDI MSI experiments. The pronounced signal enhancement due to IR-MALDI-DBD compared to IR-MALDI MSI enables mapping of nonpolar analytes with pixel resolutions down to 20 μm in mouse brain tissue and to discern the spatial distribution of sterol lipids characteristic for histological regions of D. plexippus.
- ItemInteratomic and Intermolecular Coulombic Decay(Washington, DC : ACS Publ., 2020) Jahnke, Till; Hergenhahn, Uwe; Winter, Bernd; Dörner, Reinhard; Frühling, Ulrike; Demekhin, Philipp V.; Gokhberg, Kirill; Cederbaum, Lorenz S.; Ehresmann, Arno; Knie, André; Dreuw, AndreasInteratomic or intermolecular Coulombic decay (ICD) is a nonlocal electronic decay mechanism occurring in weakly bound matter. In an ICD process, energy released by electronic relaxation of an excited atom or molecule leads to ionization of a neighboring one via Coulombic electron interactions. ICD has been predicted theoretically in the mid nineties of the last century, and its existence has been confirmed experimentally approximately ten years later. Since then, a number of fundamental and applied aspects have been studied in this quickly growing field of research. This review provides an introduction to ICD and draws the connection to related energy transfer and ionization processes. The theoretical approaches for the description of ICD as well as the experimental techniques developed and employed for its investigation are described. The existing body of literature on experimental and theoretical studies of ICD processes in different atomic and molecular systems is reviewed. © 2020 American Chemical Society
- ItemExcited-state relaxation of hydrated thymine and thymidine measured by liquid-jet photoelectron spectroscopy: experiment and simulation(Washington, DC : ACS Publications, 2015) Buchner, Franziska; Nakayama, Akira; Yamazaki, Shohei; Ritze, Hans-Hermann; Lübcke, AndreaTime-resolved photoelectron spectroscopy is performed on thymine and thymidine in aqueous solution to study the excited-state relaxation dynamics of these molecules. We find two contributions with sub-ps lifetimes in line with recent excited-state QM/MM molecular dynamics simulations (J. Chem. Phys.2013, 139, 214304). The temporal evolution of ionization energies for the excited ππ* state along the QM/MM molecular dynamics trajectories were calculated and are compatible with experimental results, where the two contributions correspond to the relaxation paths in the ππ* state involving different conical intersections with the ground state. Theoretical calculations also show that ionization from the nπ* state is possible at the given photon energies, but we have not found any experimental indication for signal from the nπ* state. In contrast to currently accepted relaxation mechanisms, we suggest that the nπ* state is not involved in the relaxation process of thymine in aqueous solution.
- ItemIntracycle interference in ionization of Ar by a laser assisted XUV pulse(Bristol : IOP Publ., 2017) Arbó, D.G.; López, S. D.; Kubin, M.; Hummert, J.; Vrakking, M.J.J.; Kornilov, O.Synopsis We present a theoretical and experimental study of the subcycle interference in laser assisted XUV ionization of Ar atoms. Averaging over the focal volume happens to blur the intracycle interference, which thus cannot be measured directly. We show that even at these conditions, the intracycle interference can be obtained through the subtraction of two different angle and energy-resolved distributions at slightly different laser intensities.
- ItemAbove-threshold ionization in a bicircular field: Quantum orbits unfolding in a plane(Bristol : IOP Publ., 2017) Becker, W.; Milošević, D.B.Above-threshold ionization (ATI) of atoms by a strong bicircular laser field is investigated using the strong-field approximation and the quantum-orbit theory. The bicircular field consists of two coplanar counterrotating circularly polarized fields with a frequency ratio of 2:1. The velocity map of the angle-resolved ATI spectra, both for direct and rescattered electrons, reflects the shape of a parametric plot of the bicircular field and its symmetries. It is shown that the main characteristics of the ATI spectra can be explained using only a few quantum orbits having short travel times. We also analyze a recently discovered [Phys. Rev. A 93, 052402(R) (2016)] bicircular-field-induced spin asymmetry of the ATI electrons and show that the momentum dependence of the spin-asymmetry parameter is stronger for longer wavelengths.
- ItemIntracluster Coulombic decay following intense NIR ionization of clusters(Bristol : IOP Publ., 2015) Schütte, Bernd; Arbeiter, Mathias; Fennel, Thomas; Jabbari, Ghazal; Gokhberg, Kirill; Kuleff, Alexander I.; Vrakking, Marc J. J.; Rouzée, ArnaudWe report on the observation of a novel intracluster Coulombic decay process following Rydberg atom formation in clusters ionized by intense near-infrared fields. A new decay channel emerges, in which a Rydberg atom relaxes to the ground state by transferring its excess energy to a weakly bound electron in the environment that is emitted from the cluster. We find evidence for this process in the electron spectra, where a peak close to the corresponding atomic ionization potential is observed. For Ar clusters, a decay time of 87 ps is measured, which is significantly longer than in previous time-resolved studies of interatomic Coulombic decay.
- ItemUnified description of low-order above-threshold ionization on and off axis(Bristol : IOP Publ., 2016) Becker, W.; Milošević, D.B.A recently developed unified description of low-order above-threshold ionization (Becker et al 2014 J. Phys. B: At. Mol. Opt. Phys. 47 204022; 2015 J. Phys. B: At. Mol. Opt. Phys. 48 151001) is revisited and extended. By considering the rescattering electron energies and angles at the classical cutoffs and the contributions of particular quantum-orbit solutions, it is shown that summing both the backward- and the forward-scattering contributions, within the low-frequency approximation, it is possible to reproduce the observed features of the ATI spectra both for low and high energies and both on and off the laser-polarization axis in the momentum plane.
- ItemCorrelated electronic decay following intense near-infrared ionization of clusters(Bristol : IOP Publ., 2015) Schütte, Bernd; Arbeiter, Mathias; Fennel, Thomas; Jabbari, Ghazal; Kuleff, Alexander I.; Vrakking, Marc J. J.; Rouzée, ArnaudWe report on a novel correlated electronic decay process following extensive Rydberg atom formation in clusters ionized by intense near-infrared fields. A peak close to the atomic ionization potential is found in the electron kinetic energy spectrum. This new contribution is attributed to an energy transfer between two electrons, where one electron decays from a Rydberg state to the ground state and transfers its excess energy to a weakly bound cluster electron in the environment that can escape from the cluster. The process is a result of nanoplasma formation and is therefore expected to be important, whenever intense laser pulses interact with nanometer-sized particles.
- ItemA multiwavelength study of the Stingray Nebula; properties of the nebula, central star, and dust(Bristol : IOP Publ., 2016) Otsuka, Masaaki; Parthasarathy, Mudumba; Tajitsu, Akito; Hubrig, SwetlanaWe performed a detail chemical abundance analysis and photo-ionization modeling of the Stingray Nebula (Hen3-1357, Parthasarathy et al. 1993[1]) to more characterize this PN. We calculated nine elemental abundances using collisionally excited lines (CELs) and recombination lines (RLs). The RL C/O ratio indicates that this PN is O-rich, which is supported by the detection of the broad amorphous silicate features at 9 and 18 μm By photo-ionization modeling, we investigated properties of the central star and derived the gas and dust masses. The nebular elemental abundances, the core-mass of the central star, and the gas mass are in agreement with the AGB model for the initially 1.5 M⊙ stars with the Z = 0.008.
- ItemMolecular above-threshold ionization spectra as an evidence of the three-point interference of electron wave packets(Bristol : IOP Publ., 2015) Hasović, Elvedin; Milošević, Dejan B.; Gazibegović-Busuladži, Azra; Čerkić, Aner; Busuladžić, MustafaWe consider high-order above-threshold ionization (HATI) of polyatomic molecules ionized by a strong linearly polarized laser field. Improved molecular strong-field approximation by which the HATI process on polyatomic molecular species can be described is developed. Using this theory we calculate photoelectron angular-energy spectra for different triatomic molecules. Special attention is devoted to the minima that are observed in the calculated high-energy electron spectra of the ozone and carbon dioxide molecules. A key difference between these minima and minima that are observed in the corresponding spectra of diatomic molecules are presented.