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Among the numerous constituents of eukaryotic cells, the DNA macromolecule is considered as the most important critical target for radiation-induced damages. However, up to now ion-induced collisions on DNA components remain scarcely approached and theoretical support is still lacking for describing the main ionizing processes. In this context, we here report a theoretical description of the proton-induced ionization of the DNA and RNA bases as well as the sugar-phosphate backbone. Two different quantum-mechanical models are proposed: the first one based on a continuum distorted wave-eikonal initial state treatment and the second perturbative one developed within the first Born approximation with correct boundary conditions (CB1). Besides, the molecular structure information of the biological targets studied here was determined by ab initio calculations with the Gaussian 09 software at the restricted Hartree-Fock level of theory with geometry optimization. Doubly, singly differential and total ionization cross sections also provided by the two models were compared for a large range of incident and ejection energies and a very good agreement was observed for all the configurations investigated. Finally, in comparison with the rare experiment, we have noted a large underestimation of the total ionization cross sections of uracil impacted by 80 keV protons,whereas a very good agreement was shown with the recently reported ionization cross sections for protons on adenine, at both the differential and the total scale.

Quasiclassical trajectory and quantum-mechanical scattering calculations are reported for the O(³P)+H2(X ¹Σg + ; υ=1-3, j=0)→?OH(X ²II)+H(²S) reaction at energies close to the reaction threshold. The dynamics of the reaction have been investigated for zero total angular momentum using the lowest ³A" potential-energy surface developed by Rogers et al. [J. Phys. Chem. A 104, 2308 (2000)] and its recent extensions by Brandão et al. [J. Chem. Phys. 121, 8861 (2004)] which provide an improved description of the van der Waals interaction. Good agreement is observed for this system between quasiclassical and quantal results for incident kinetic energies above the tunneling regime. Quantum-mechanical calculations also confirm recent theoretical predictions of a strong collision-energy dependence of the OH(υ'=0)/OH(υ'=1) product branching ratio in the O(³P)+H2(υ=1) reaction, which explains the differences observed in OH vibrational populations between experiments using different O(³P) sources. [ABSTRACT FROM AUTHOR]

Quantum-mechanical calculations are reported for the Li+HF(v=0,1,j=0)→H+LiF(v′,j′) bimolecular scattering process at low and ultralow temperatures. Calculations have been performed for zero total angular momentum using a recent high-accuracy potential-energy surface for the X2A′ electronic ground state. For Li+HF(v=0,j=0), the reaction is dominated by resonances due to the decay of metastable states of the Li...F–H van der Waals complex. Assignment of these resonances has been carried out by calculating the eigenenergies of the quasibound states. We also find that while chemical reactivity is greatly enhanced by vibrational excitation, the resonances get mostly washed out in the reaction of vibrationally excited HF with Li atoms. In addition, we find that at low energies, the reaction is significantly suppressed due to the less-efficient tunneling of the relatively heavy fluorine atom. [ABSTRACT FROM AUTHOR]