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MO: Molekülphysik
MO 29: Poster: Biomolecules
MO 29.2: Poster
Tuesday, March 14, 2006, 16:30–18:30, Labsaal
Stability of uracil and thymine cations — •Manuel Beikircher1, Sylwia Ptasinska1, Stefan Feil1, Manuel Winkler1, Arntraud Bacher1, Werner Schustereder2, Stephan Denifl1, Olof Echt3, Tilmann D. Märk1, and Paul Scheier1 — 1Institut für Ionenphysik,Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria — 2Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany — 3Department of Physics, University of New Hampshire, Durham, USA
Attachment of free electrons to uracil and thymine leads exclusively to the formation of fragment anions and the most abundant product are (U-H)- and (T-H)-, respectively [1]. However, in the positive mass spectrum of these molecules no H-loss is observed. This is in contrast to electron impact ionization of hydrocarbons where H-loss is an important process. In the present study H-loss from excited uracil cations has been discovered and the resulting ion (U-H)+ is observed to decay quickly into more stable products upon ring dissociation. The measurements are performed utilizing a modified VG-ZAB mass spectrometer in reversed geometry. The uracil and thymine molecules are ionized by electron impact at 74 eV. The ions are then accelerated at different acceleration voltages, from 1 to 10 kV, resulting in different flight times to the detector. By decoupling the two sector fields single decay processes are studied in two different windows and even the sequential decay of metastable uracil can unambiguously be identified.
[1] S. Denifl, S. Ptasinska, M. Probst, J. Hrusak, P. Scheier and T.D. Märk, J. Phys. Chem. A 108 (2004) 6562-6569