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Low Energy Electron Interactions with Biologically Relevant Molecules P. Scheier, S. Ptasinska, S. Denifl, J. Fedor, S. Feil, Institut für Ionenphysik, Leopold-Franzens Universität
Innsbruck, The interaction of highly mono energetic electrons with molecules such as DNA and RNA bases, water, glycine, deoxyribose, glycol-aldehyde and various organic acids has been studied. Experimentally the formation of both positively and negatively charged product ions has been investigated and complementary quantum chemical calculations were performed. The aim of these studies is to understand the basic processes that lead finally to the damage of living cells upon exposure to ionizing radiation (a, b, g, ions). Sanche and co-workers [1] recently demonstrated that potentially lethal DNA damage (double strand breaks) can be induced by low energy electrons. They observed a well pronounced maximum in the yield of single and double strand breaks at electron energies of 10 eV. Such resonances are typical for the formation of fragment anions. In the present experiment gas phase biomolecules that were vaporized in an oven are crossed with an electron beam with narrow energy spread (~100meV). The dominant negative ions formed via free electron attachment reactions to most of the molecules M studies so far (exceptions are halogenated uracil, water and sugar) are the closed shell anions (M-H)– [2] The attachment cross sections of these anions have a maximum value between 1 eV and 1.5 eV and in several cases we observed a series of narrow peaks. In the case of thymine (T) we could identify experimentally the position of the molecule where the hydrogen atoms were removed by using partially deuterated molecules. For three different reaction channels, i.e. (T-H)–, (T-2H)– and H– we could observe characteristic bond selectivity for several resonances. The next step towards more complex biomolecules has already been taken. We investigated electron impact ionization and dissociative electron attachment of thymidine and uridine. These molecules consist of a base and a sugar molecule. Using a two sector field mass spectrometer we recently started to investigate delayed unimolecular decomposition of product ions formed via inelastic interactions of electrons with biomolecules. Work partially supported by the FWF, ÖAW and ÖNB, Wien, Austria and the European Commission, Brussels. |
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