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Abstract English

Laboratory measurements are proposed to investigate dissociative electron attachment (DEA) to DNA bases and nitrotoluene and their derivatives. For most of the biologically relevant molecules studied so far, neutral H loss and the formation of H– are important DEA channels. Very recent studies on the H– loss from several organic molecules, including the phyrimidine bases uracil and thymine, demonstrate that by tuning the electron energy it is possible to selectively break a specific bond. Isotopically labeled molecules and methylated derivates enable experimentally the assignment of resonances to bond breaking at specific molecular sites. In the presently proposed studies it is planned to investigate site selectivity of neutral H and H– loss from the other DNA bases, i.e., adenine, cytosine and guanine. For NO2–, the most abundant fragment anion formed via DEA to various nitrotoluene molecules, site selectivity has been described in the literature, i.e., the energy and intensity of the resonances depend strongly on the position of the NO2 group relative to the methyl group. For several heavy fragment anions formed via DEA to various nitrotoluene molecules we discovered similar site selectivity. Again labeling with isotopes and functional groups is planned to assign the resonances in the attachment cross sections to bond rupture at a specific site. A pulsed hemispherical electron monochromator will be built. The interaction region between electrons and neutral target molecules will be field-free when electrons are present which is essential for high electron energy resolution. However, a strong extraction field in the time when the electron beam is off can be used to collect all ions with uniform efficiency, even if they are formed with a high kinetic energy. Furthermore, it is planned to utilize this pulsed ion source to measure the kinetic energy that is released in the DEA process. In the case of one atomic fragment, such as the H– formation, the kinetic energy of the anion determines the internal energy that remains in the heavy fragment. In extension to simple gas phase experiments it is planned to study free electron attachment to clusters of the molecules mentioned above or to molecules embedded in a well defined solvent layer. For this purpose two recently constructed neutral beam sources will be utilized, i.e., a helium cluster source and a spray source. Thereby the signature of site selective DEA channels on secondary reaction products resulting from intra-cluster anion molecule reactions will be studied. In the case of biomolecules clusters and complexes with water will bridge the gap between gas phase studies and the investigation of low-energy electron induced DNA strand breaks. Furthermore, free electron interactions with ultra-cold targets of water and biomolecules, formed via pick-up of superfluid He droplets, can give important insight into the formation, liberation and destruction of complex organic molecules in dense interstellar clouds.

 

Abstract German

german abstract