TY - JOUR A1 - Riebe, Daniel A1 - Eder, Alexander A1 - Ritschel, Thomas A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Beil, Andreas A1 - Blaschke, Michael A1 - Ludwig, Thomas T1 - Atmospheric pressure chemical ionization of explosives induced by soft X-radiation in ion mobility spectrometry: mass spectrometric investigation of the ionization reactions of drift gasses, dopants and alkyl nitrates JF - Journal of mass spectrometr N2 - A promising replacement for the radioactive sources commonly encountered in ion mobility spectrometers is a miniaturized, energy-efficient photoionization source that produce the reactant ions via soft X-radiation (2.8 keV). In order to successfully apply the photoionization source, it is imperative to know the spectrum of reactant ions and the subsequent ionization reactions leading to the detection of analytes. To that end, an ionization chamber based on the photoionization source that reproduces the ionization processes in the ion mobility spectrometer and facilitates efficient transfer of the product ions into a mass spectrometer was developed. Photoionization of pure gasses and gas mixtures containing air, N-2, CO2 and N2O and the dopant CH2Cl2 is discussed. The main product ions of photoionization are identified and compared with the spectrum of reactant ions formed by radioactive and corona discharge sources on the basis of literature data. The results suggest that photoionization by soft X-radiation in the negative mode is more selective than the other sources. In air, adduct ions of O-2 - with H2O and CO2 were exclusively detected. Traces of CO2 impact the formation of adduct ions of O-2 - and Cl -(upon addition of dopant) and are capable of suppressing them almost completely at high CO2 concentrations. Additionally, the ionization products of four alkyl nitrates (ethylene glycol dinitrate, nitroglycerin, erythritol tetranitrate and pentaerythritol tetranitrate) formed by atmospheric pressure chemical ionization induced by X-ray photoionization in different gasses (air, N-2 and N2O) and dopants (CH2Cl2, C2H5Br and CH3I) are investigated. The experimental studies are complemented by density functional theory calculations of the most important adduct ions of the alkyl nitrates (M) used for their spectrometric identification. In addition to the adduct ions [M + NO3](-) and [M + Cl](-), adduct ions such as [M + N2O2](-), [M + Br](-) and [M+ I](-) were detected, and their gas-phase structures and energetics are investigated by density functional theory calculations. Copyright (C) 2016 John Wiley & Sons, Ltd. KW - ion mobility spectrometry KW - mass spectrometry KW - explosives KW - X-ray KW - photoionization KW - alkyl nitrates Y1 - 2016 U6 - https://doi.org/10.1002/jms.3784 SN - 1076-5174 SN - 1096-9888 VL - 51 SP - 566 EP - 577 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Mahapatra, Susanta A1 - Vetter, Reinhard A1 - Zuhrt, Christian A1 - Nguyen, Huu Tong A1 - Ritschel, Thomas A1 - Zülicke, Lutz T1 - Bound states and time-dependent dynamics of the N2H+ molecular ion in its ground electronic state. I. 2D treatment Y1 - 1997 ER - TY - JOUR A1 - Ritschel, Thomas A1 - Zülicke, Lutz A1 - Kuntz, Philip J. T1 - Cationic Van-der-Waals complexes : theoretical study of Ar2H+ structure and stability N2 - The electronic and geometric structure, stability and molecular properties of the cationic van-der-Waals complex Ar2H+ in its ground electronic state are studied by means of two ab-initio quantum-chemical approaches: conventional configuration interaction (multi-reference and coupled cluster methods) and a diatomics-in-molecules model with ab-initio input data. Y1 - 2004 ER - TY - JOUR A1 - Mahapatra, Susanta A1 - Vetter, Reinhard A1 - Zuhrt, Christian A1 - Nguyen, Huu Tong A1 - Ritschel, Thomas A1 - Zülicke, Lutz T1 - Ground state potential energy surface, 3D time-dependent intramolecular dynamics and vibrational states of the N2H+ molecular ion Y1 - 1998 ER - TY - JOUR A1 - Primus, Philipp-Alexander A1 - Ritschel, Thomas A1 - Sigueenza, Pilar Y. A1 - Cauqui, Miguel Angel A1 - Hernandez-Garrido, Juan Carlos A1 - Kumke, Michael Uwe T1 - High-resolution spectroscopy of europium-doped ceria as a tool to correlate structure and catalytic activity JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Site-selective emission spectra of Eu3+-doped CeO2 nanoparticles up to the D-5(0) - F-7(5) transition were recorded under cryogenic conditions to identify the local structure around the Eu3+ dopants in ceria. It is found that pretreatment conditions are crucial for the redistribution of dopants from a broad variety of environments to six well-defined lattice sites. The influence of the dopant and the host structure on the catalytic activity was investigated. A relationship between structure and reactivity is discussed. It is shown that oxygen transport is most efficient in particles with a pronounced amorphous character. Y1 - 2014 U6 - https://doi.org/10.1021/jp505467r SN - 1932-7447 VL - 118 IS - 40 SP - 23349 EP - 23360 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Gianturco, Franco A. A1 - Kumar, Sanjay A1 - Vetter, Reinhard A1 - Ritschel, Thomas A1 - Zülicke, Lutz T1 - Interaction anisotropy and vibrational excitation in proton scattering from N2(1sigma g+) Y1 - 1997 ER - TY - JOUR A1 - Brendler, Christian A1 - Riebe, Daniel A1 - Ritschel, Thomas A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd T1 - Investigation of neuroleptics and other aromatic compounds by laser-based ion mobility mass spectrometry JF - Analytical & bioanalytical chemistry N2 - Laser-based ion mobility (IM) spectrometry was used for the detection of neuroleptics and PAH. A gas chromatograph was connected to the IM spectrometer in order to investigate compounds with low vapour pressure. The substances were ionized by resonant two-photon ionization at the wavelengths lambda = 213 and 266 nm and pulse energies between 50 and 300 mu J. Ion mobilities, linear ranges, limits of detection and response factors are reported. Limits of detection for the substances are in the range of 1-50 fmol. Additionally, the mechanism of laser ionization at atmospheric pressure was investigated. First, the primary product ions were determined by a laser-based time-of-flight mass spectrometer with effusive sample introduction. Then, a combination of a laser-based IM spectrometer and an ion trap mass spectrometer was developed and characterized to elucidate secondary ion-molecule reactions that can occur at atmospheric pressure. Some substances, namely naphthalene, anthracene, promazine and thioridazine, could be detected as primary ions (radical cations), while other substances, in particular acridine, phenothiazine and chlorprothixene, are detected as secondary ions (protonated molecules). The results are interpreted on the basis of quantum chemical calculations, and an ionization mechanism is proposed. KW - Ion mobility spectrometry KW - Mass spectrometry KW - Gas chromatography KW - Laser ionization KW - REMPI KW - Neuroleptics Y1 - 2013 U6 - https://doi.org/10.1007/s00216-012-6654-7 SN - 1618-2642 VL - 405 IS - 22 SP - 7019 EP - 7029 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Mahapatra, Susanta A1 - Ritschel, Thomas T1 - Multistate vibronic interactions and nonadiabatic wave packet dynamics in the second photoelectron band of chlorine dioxide N2 - We report theoretical investigations on the second photoelectron band of chlorine dioxide molecule by ab initio quantum dynamical methods. This band exhibits a highly complex structure and represents a composite portrait of five excited energetically close-lying electronic states of ClO2+. Much of this complexity is likely to be arising due to strong vibronic interactions among these electronic states - which we address and examine herein. The near equilibrium MRCI potential energy surfaces (PESs) of these five cationic states reported by Peterson and Werner [J. Chem. Phys. 99 (1993) 302] for the C2v configuration, are extended for the Cs geometry assuming a harmonic vibration along the asymmetric stretching mode. The strength of the vibronic coupling parameters of the Hamiltonian are calculated by ab initio CASSCF-MRCI method and conical intersections of the PESs are established. The diabatic Hamiltonian matrix is constructed within a linear vibronic coupling scheme and the resulting PESs are employed in the nuclear dynamical simulations, carried out with the aid of a time-dependent wave packet approach. Companion calculations are performed for transitions to the uncoupled electronic states in order to reveal explicitly the impact of the nonadiabatic coupling on the photoelectron dynamics. The theoretical findings are in good accord with the experimental observations. The femtosecond nonradiative decay dynamics of ClO2+ excited electronic states mediated by conical intersections is also examined and discussed. Y1 - 2003 ER - TY - JOUR A1 - Kupstat, Annette A1 - Ritschel, Thomas A1 - Kumke, Michael Uwe T1 - Oxazine Dye-Conjugated DNA Oligonucleotides Forster Resonance Energy Transfer in View of Molecular Dye-DNA Interactions JF - Bioconjugate chemistry N2 - In this work, the photophysical properties of two oxazine dyes (ATTO 610 and ATTO 680) covalently attached via a C6-amino linker to the 5'-end of short single-stranded as well as double-stranded DNA (ssDNA and dsDNA, respectively) of different lengths were investigated. The two oxazine dyes were chosen because of the excellent spectral overlap, the high extinction coefficients, and the high fluorescence quantum yield of ATTO 610, making them an attractive Forster resonance energy transfer (FRET) pair for bioanalytical applications in the far-red spectral range. To identify possible molecular dye-DNA interactions that cause photophysical alterations, we performed a detailed spectroscopic study, including time-resolved fluorescence anisotropy and fluorescence correlation spectroscopy measurements. As an effect of the DNA conjugation, the absorption and fluorescence maxima of both dyes were bathochromically shifted and the fluorescence decay times were increased. Moreover, the absorption of conjugated ATTO 610 was spectrally broadened, and a dual fluorescence emission was observed. Steric interactions with ssDNA as well as dsDNA were found for both dyes. The dye-DNA interactions were strengthened from ssDNA to dsDNA conjugates, pointing toward interactions with specific dsDNA domains (such as the top of the double helix). Although these interactions partially blocked the dye-linker rotation, a free (unhindered) rotational mobility of at least one dye facilitated the appropriate alignment of the transition dipole moments in doubly labeled ATTO 610/ATTO 680-dsDNA conjugates for the performance of successful FRET. Considering the high linker flexibility for the determination of the donor-acceptor distances, good accordance between theoretical and experimental FRET parameters was obtained. The considerably large Forster distance of similar to 7 nm recommends the application of this FRET pair not only for the detection of binding reactions between nucleic acids in living cells but also for monitoring interactions of larger biomolecules such as proteins. Y1 - 2011 U6 - https://doi.org/10.1021/bc200379y SN - 1043-1802 VL - 22 IS - 12 SP - 2546 EP - 2557 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Ritschel, Thomas A1 - Mahapatra, Susanta A1 - Zülicke, Lutz T1 - Quasiclassical dynamics of proton scattering by N2 on an improved ab initio potential energy surface N2 - An improved analytical representation of the ground electronic potential energy surface (PES) of the (H+, N2) system is generated using the ab initio data reported in our earlier work. The new analytical PES function describes adequately the global behavior and in particular the angular dependence of the interaction as well as the long-range part so that it is amenable to scattering studies. We investigate the elastic and inelastic H+-N2 scattering dynamics on this PES by the quasiclassical trajectory method for center-of-mass collision energies in the range 29-144 eV. The trajectory results thus obtained are compared with the available experimental findings and with recent quantum-mechanical (vibrational close-coupling rotational infinite-order sudden) results. Despite some differences, the experimental data are well reproduced by the present calculations. Y1 - 2001 ER -