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Electron loss from the four DNA nucleobases, namely, adenine, cytosine, thymine, and guanine as well as from RNA uracil base produced by high-energy impact of multiply charged bare ions are here theoretically investigated via a simple model combining two classical approximations-the classical trajectory Monte Carlo and the classical overbarrier-previously used with success to describe the ionization of water molecules by ions. We give in the present work an estimation of the single-electron ionization and single-electron capture cross sections for different incident projectiles, namely, H + , He 2+ , and C 6+ ions with impact energies ranging from 10 keV/amu to 10 MeV/amu. The obtained results are compared to the rare theoretical predictions available in the literature and therefore highlight binding effects whose existence has been already demonstrated in the case of atomic collisions but not for ͑so͒ large molecular systems.

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Induction of DNA double strand breaks after irradiation is considered of prime importance for producing radio-induced cellular death or injury. However, up to now ion-induced collisions on DNA bases remain essentially experimentally approached and a theoretical model for cross section calculation is still lacking. Under these conditions, we here propose a quantum mechanical description of the ionization process induced by light bare ions on DNA bases. Theoretical predictions in terms of differential and total cross sections for proton, α-particle and bare ion carbon beams impacting on adenine, cytosine, thymine and guanine bases are then reported in the 10 keV amu(-1)-10 MeV amu(-1) energy range. The calculations are performed within the first-order Born approximation (FBA) with biological targets described at the restricted Hartree-Fock level with geometry optimization. Comparisons to recent theoretical data for collisions between protons and cytosine point out huge discrepancies in terms of differential as well as total cross sections whereas very good agreement is shown with our previous classical predictions, especially at high impact energies (E(i) ≥ 100 keV amu(-1)). Finally, in comparison to the rare existing experimental data a systematic underestimation is observed in particular for adenine and thymine whereas a good agreement is reported for cytosine. Thus, further improvements appear as necessary, in particular by using higher order theories like the continuum-distorted-wave one in order to obtain a better understanding of the underlying physics involved in such ion-DNA reactions.