@article{AwasthiRitschelLipowskyetal.2013,
  author    = {Awasthi, Neha and Ritschel, Thomas and Lipowsky, Reinhard and Knecht, Volker},
  title     = {Standard gibbs energies of formation and equilibrium constants from ab-initio calculations covalent dimerization of NO2 and synthesis of NH3},
  series = {The journal of chemical thermodynamics},
  volume    = {62},
  journal   = {The journal of chemical thermodynamics},
  number    = {3},
  publisher = {Elsevier},
  address   = {London},
  issn      = {0021-9614},
  doi       = {10.1016/j.jct.2013.03.011},
  pages     = {211 -- 221},
  year      = {2013},
  abstract  = {Standard quantum chemical methods are used for accurate calculation of thermochemical properties such as enthalpies of formation, entropies and Gibbs energies of formation. Equilibrium reactions are widely investigated and experimental measurements often lead to a range of reaction Gibbs energies and equilibrium constants. It is useful to calculate these equilibrium properties from quantum chemical methods in order to address the experimental differences. Furthermore, most standard calculation methods differ in accuracy and feasibility of the system size. Hence, asystematic comparison of equilibrium properties calculated with different numerical algorithms would provide a useful reference. We select two well-known gas phase equilibrium reactions with small molecules: covalent dimer formation of NO2 (2NO(2) reversible arrow N2O4) and the synthesis of NH3 (N-2 + 3 H-2 reversible arrow 2NH(3)). We test four quantum chemical methods denoted by G3B3, CBS-APNO, W1 and CCSD(T) with aug-cc-pVXZ basis sets (X = 2, 3, and 4), to obtain thermochemical data for NO2, N2O4, and NH3. The calculated standard formation Gibbs energies Delta(f)G degrees are used to calculate standard reaction Gibbs energies Delta(r)G degrees and standard equilibrium constants K-eq for the two reactions. Standard formation enthalpies Delta H-f degrees are calculated in a more reliable way using high-level methods such as W1 and CCSD(T). Standard entropies S degrees for the molecules are calculated well within the range of experiments for all methods, however, the values of standard formation Gibbs energies Delta(f)G degrees show some dependence on the choice of the method. High-level methods perform better for the calculation of molecular energies, however, simpler methods such as G3B3 and CBS-APNO perform quite well in the calculation of total reaction energies and equilibrium constants, provided that the chemical species involved do not exhibit molecular geometries that are difficult to handle by the applied method. The temperature dependence of standard reaction Gibbs energy Delta(r)G degrees for the NH3 reaction is discussed by using the calculated standard formation Gibbs energies Delta(f)G degrees of the reaction species at 298.15 K. The corresponding equilibrium constant K-eq as a function of temperature is found to be close to experimental values.},
  language  = {en}
}
@article{BrendlerRiebeRitscheletal.2013,
  author    = {Brendler, Christian and Riebe, Daniel and Ritschel, Thomas and Beitz, Toralf and L{\"o}hmannsr{\"o}ben, Hans-Gerd},
  title     = {Investigation of neuroleptics and other aromatic compounds by laser-based ion mobility mass spectrometry},
  series = {Analytical \& bioanalytical chemistry},
  volume    = {405},
  journal   = {Analytical \& bioanalytical chemistry},
  number    = {22},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1618-2642},
  doi       = {10.1007/s00216-012-6654-7},
  pages     = {7019 -- 7029},
  year      = {2013},
  abstract  = {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.},
  language  = {en}
}