We demonstrate that electrons at energies below the threshold for electronic excitation (<3 eV) effectively decompose gas phase uracil generating a mobile hydrogen radical and the corresponding closed shell uracil fragment anion (U-H)(-). The reaction is energetically driven by the large electron affinity of the (U-H) radical. This observation has significant consequences for the molecular picture of radiation damage, i.e., genotoxic effects or damage of living cells due to the secondary component of high energy radiation.

Proton transfer reaction - mass spectrometry (PTR-MS) has become a reference technique in environmental science allowing for VOC monitoring with low detection limits. The recent introduction of time-of-flight mass analyzer (PTR-ToF-MS) opens new horizons in terms of mass resolution, acquisition time, and mass range. A standard procedure to perform quantitative VOC measurements with PTR-ToF-MS is to calibrate the instrument using a standard gas. However, given the number of compounds that can be simultaneously monitored by PTR-ToF-MS, such a procedure could become impractical, especially when standards are not readily available. In the present work we show that, under particular conditions, VOC concentration determinations based only on theoretical predictions yield good accuracy. We investigate a range of humidity and operating conditions and show that theoretical VOC concentration estimations are accurate when the effect of water cluster ions is negligible. We also show that PTR-ToF-MS can successfully be used to estimate reaction rate coefficients between H(3)O(+) and VOC at PTR-MS working conditions and find good agreement with the corresponding nonthermal theoretical predictions. We provide a tabulation of theoretical rate coefficients for a number of relevant volatile organic compounds at various energetic conditions and test the approach in a laboratory study investigating the oxidation of alpha-pinene.

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We present a detailed study on dissociative electron attachment (DEA) to isolated gas-phase cytosine (C) and thymine (T). The experimental setup used for these measurements is a crossed electron/neutral beam instrument combined with a quadrupole mass spectrometer. Electron attachment to these biomolecules leads to dissociation into various fragments without a hint of any measurable amount of stable C or T parent anions. The fragment anions with highest abundance are (C-H)and (T-H) -, respectively. Quantum chemical calculations were performed to calculate the electron affinities and binding energies of the different isomers of the (T-H) fragment. Besides (C-H)and (T-H) -, we observed five other fragment anions formed by DEA to cytosine and eight additional product anions were detected in the case of thymine. Ion efficiency curves were measured for all fragment anions in the electron energy range from about 0 to 14 eV. For mixtures of T or C with SF 6 or CCl 4 in the collision chamber, additional resonances close to 0 eV were observed, resulting from ion molecule reactions of SF 6or Clwith the respective biomolecule.

An improved central force model for water recently developed was used to perform a molecular dynamics simulation of a 1.1 m aqueous CaC12 solution at the experimental density at room temperature. The ion-water potentials were derived from ab initio calculations. The solution was simulated for 10 ps at 300 K. A new X-ray scattering study of a CaClz solution was performed at the same concentration and temperature. The structure function and the radial distribution function were evaluated with geometrical models. The comparison between experimental and theoretical results is performed on the level both of the structure function and of the interparticle radial pair distribution functions. More detailed results about the structure of the cationic hydration shell are also presented and compared with results of other recent simulation and neutron diffraction work.