Microscopic studies of atom–water collisions (original) (raw)
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Exploration of dynamical regimes of irradiated small protonated water clusters
The European Physical Journal D, 2010
We explore from a theoretical perspective the dynamical response of small water clusters, (H2O)nH3O + with n = 1, 2, 3, to a short laser pulse for various frequencies, from infrared (IR) to ultraviolet (UV) and intensities (from 6 × 10 13 W/cm 2 to 5 × 10 14 W/cm 2). To that end, we use time-dependent local-density approximation for the electrons, coupled to molecular dynamics for the atomic cores (TDLDA-MD). The local-density approximation is augmented by a self-interaction correction (SIC) to allow for a correct description of electron emission. For IR frequencies, we see a direct coupling of the laser field to the very light H + ions in the clusters. Resonant coupling (in the UV) and/or higher intensities lead to fast ionization with subsequent Coulomb explosion. The stability against Coulomb pressure increases with system size. Excitation to lower ionization stages induced strong ionic vibrations. These maintain rather harmonic pattern in spite of the sizeable amplitudes (often 10% of the bond length).
Theoretical treatment of direct and indirect processes in ion‐biomolecule collisions
2008
Test case collision systems for direct and indirect processes in the action of radiation on the biological medium have been investigated theoretically by means of ab initio quantum chemistry molecular methods followed by a semiclassical dynamical treatment. As a direct process, we have studied the charge transfer of the RNA base uracil on C q+ ions (q=2,4). The process depends strongly on the orientation of the projectile towards the uracil target, in particular for the C 4+ + uracil reaction, and shows a significant delocalization of the π electrons of the uracil ring towards the carbon ion. The collision of C 2+ ions on the OH radical has been also investigated as a model of the action of ions on OH radicals created in the medium, in order to have a look to some possible indirect processes. The approach in the linear geometry with consideration of the relaxation of the OH target has been considered.
Molecular Physics, 2014
Proton cancer therapy (PCT) utilises high-energy H + projectiles to cure cancer. PCT healing arises from its DNA damage in cancerous cells, which is mostly inflicted by the products from PCT water radiolysis reactions. While clinically established, a complete microscopic understanding of PCT remains elusive. To help in the microscopic elucidation of PCT, ProfessorÖhrn's simplest-level electron nuclear dynamics (SLEND) method is herein applied to H + + (H 2 O) 3-4 and H + + DNA-bases at E Lab = 1.0 keV. These are two types of computationally feasible prototypes to study water radiolysis reactions and H +-induced DNA damage, respectively. SLEND is a time-dependent, variational, non-adiabatic and direct-dynamics method that adopts a nuclear classical-mechanics description and an electronic single-determinantal wavefunction. Additionally, our SLEND + effective-core-potential method is herein employed to simulate some computationally demanding PCT reactions. Due to these attributes, SLEND proves appropriate for the simulation of various types of PCT reactions accurately and feasibly. H + + (H 2 O) 3-4 simulations reveal two main processes: H + projectile scattering and the simultaneous formation of H and OH fragments; the latter process is quantified through total integrals cross sections. H + + DNA-base simulations reveal atoms and groups displacements, ring openings and base-to-proton electron transfers as predominant damage processes.
Physical Review A, 2013
Two nonperturbative methods are applied to obtain total and singly differential (in the electron energy) cross sections of electron emission in proton collisions with H 2 O at impact energies in the range 10 keV E p 5 MeV. Both methods, one classical and one semiclassical, combine an independent particle treatment with a multicenter model potential description of the target. The excellent agreement obtained with experimental data supports the usefulness of the approximations involved and encourages the study of more complex systems.
2009
Monte Carlo codes for ion-nanodosimetry in tissue-like media require a detailed knowledge of the ionization cross sections. Secondary electrons play a main role in the radiobiological effectiveness of any radiation. The HKS and CDW-EIS formalisms are implemented to determine single ionization cross sections (SICS) corresponding to the impact of H^+, He^2+ and C^6+ ions on liquid water, for incident energies from 0.3 to 10 MeV/u. Corrected expressions for the HKS method have been used. The same kind of initial electron wave functions and binding energies have been used with both models, in order to compare the formalisms themselves. Double and single differential as well as total SICS of liquid water have been calculated by use of both methods and comparisons have been made between their theoretical predictions. Also, these results have been compared with experimental values reported previously for ionization of water vapor due to protons and alpha particles. The excitation cross sections are included to determine electronic stopping cross sections in liquid water. The results based on the CDW- EIS method provide the best agreement when stopping powers are compared with corresponding data published in ICRU reports, obtaining discrepancies of about 9 %, 16 % and 19 % for incident protons, alpha particles and carbon ions respectively.
Radiation damage on biomolecular systems: Dynamics of ion induced collision processes
Computational and Theoretical Chemistry, 2012
The collision of carbon ions on DNA and RNA bases thymine, uracil and 5-halouracil is investigated with regard to the action of radiations on the biological medium. The charge transfer process is studied theoretically in a wide collision range by means of ab initio quantum chemistry molecular methods. A strong influence of the electronic structure and charge of the C q+ projectile may be observed correlated to previous experimental studies on the ionization and fragmentation processes. The charge transfer appears markedly anisotropic in the whole energy domain, and interesting specific features may be pointed out at low energies. For 5-halouracil targets, both electronic and steric effects drive a lowering of the cross sections, inducing an enhancement of the complementary fragmentation process in good agreement with the radio sensitivity widely recognized for such biomolecules.