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Physical Review A: Atomic, Molecular and Optical Physics 81 (2010) 012711 (10 pages)
20-150 keV proton impact induced ionization of uracil: fragmentation ratios and branching ratios for electron capture and direct ionization
J. Tabet1, S. Eden2, S. Feil1, H. Abdoul-Carime1, B. Farizon1, M. Farizon1, S. Ouaskit3, T.D. Märk4

Fragmentation ratios have been measured for ionization and dissociative ionization for 20-150 keV (0.9-2.4 v0) proton collisions with gas-phase uracil molecules. Through event-by-event determination of the post-collision projectile charge, it is possible for the first time for such a key biomolecule to distinguish between electron capture (EC) by the incident proton and direct ionization (DI) without projectile neutralization. While the same fragment ion groups are observed in the mass spectrum for both processes, electron capture induces dissociation with greater efficiency than direct ionization in the impact energy range of 35-150 keV (1.2-2.4 v0). In this range electron capture is also less abundant than direct ionization with a branching ratio for electron capture / total ionization of < 50%. Moreover, whereas fragmentation ratios do not change with energy in case of electron capture, direct ionization mass spectra show a tendency for increased fragmentation at lower impact energies.
1 :  IPNL - Institut de Physique Nucléaire de Lyon
2 :  Department of Physics and Astronomy
3 :  Université Hassan II-Mohammedia, Faculté des Sciences Ben M'Sik (LPMC)
4 :  Institut für Ionenphysik und Angewandte Physik
Physique/Physique des Hautes Energies - Expérience

Uracil – proton impact – ionization – dissociative ionization – electron capture – mass spectrometry
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URACILE-SM.pdf(433.2 KB)