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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.

In this work, we report total cross sections for the single electron capture process induced on DNA/RNA bases by high-energy protons. The calculations are performed within both the continuum distorted wave and the continuum distorted wave-eikonal initial state approximations. The biological targets are described within the framework of self-consistent methods based on the complete neglect of differential overlap model whose accuracy has first been checked for simpler bio-molecules such as water vapour. Furthermore, the multi-electronic problem investigated here is reduced to a mono-electronic one using a version of the independent electron approximation. Finally, the obtained theoretical predictions are confronted with the scarcely available experimental results.

Ionization and fragmentation of uracil molecules (C 4 H 4 N 2 O 2 , m = 112 amu) in collisions with fast highly charged C, O and F ions have been investigated using a time-of-flight mass spectrometer. The measurement of total ionization cross sections (TCS) is reported for different charge states (q), such as F q+ with q = 5-8; O q+ with q = 5,7; C q+ with q = 5 and 6. These studies reveal a (q/v) ∼1.5 dependence of TCS, in contrast, to the well-known q 2 -dependence in ion-atom collisions. Scaling properties of the TCS with projectile energy and charge states are obtained. The experimental results for TCS measurements are compared with the theoretical calculations performed within classical and quantum mechanical frameworks. The trends in energy dependence of the TCSs is qualitatively well reproduced by the different models and more specifically by the classical description, which provides the best agreement with measurements.

In the current work, we present a study of ionizing interactions between protons and molecular targets of biological interest like water vapour and DNA bases. Total cross sections for single and multiple ionizing processes are calculated in the Independent Electron Model and compared to existing theoretical and experimental results for impact energies ranging from 10keV/amu to 10MeV/amu. The theoretical approach combines some characteristics of the Classical Trajectory Monte Carlo method with the Classical Over-Barrier framework. In this "mixed" approach, all the particles are described in a classical way by assuming that the target electrons are involved in the collision only when their binding energy is greater than the maximum of the potential energy of the system {projectile-target}. We test our theoretical approach on the water molecule and the obtained results are compared to a large set of data and a reasonable agreement is generally observed specially for impact energies greater than 100keV, excepted for the double ionization process for which large discrepancies are reported. Considering the DNA bases, the obtained results are given without any comparison since the literature is till now very poor in terms of cross section measurements.

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