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V Encuentro Sud Americano de Colisiones Inelásticas en la Materia Multiple differential cross sections for the ionization from the 1B 1 orbital of liquid water molecule by fast electron impact M.L. de Sanctis 1 , O. Fojón 1 , C. Stia 1 , R. Vuilleumier 2 and M.-F. Politis 3 1 Instituto de Física Rosario (CONICET-UNR), Pellegrini 250, (2000) Rosario, Argentina 2 LPTMC, UMR-CNRS 7600, Université Pierre et Marie Curie 4 place Jussieu, 75005, Paris, France 3 IMPMC, Université Pierre et Marie Curie, Campus Boucicaut, 140 rue de Lourmel, 75015, Paris, France email: mldesanc@fceia.unr.edu.ar Ionization of water molecules in liquid phase is of relevance in several domains such as radiobiology and medical physics. As the biological matter is composed mainly of water, the analysis of this reaction is crucial to understand the damage provoked to living tissue by the ionizing radiations. In particular, the production of low energy secondary electrons resulting from a primary ionization reaction of water is of importance to elucidate the mechanisms that lead to cell alteration. Therefore, we study the single ionization of water molecules in liquid phase by electron impact at high impact energies, i.e., hundreds of eV. We compute multiple differential cross sections (MDCS) by means of a simple first order model. To represent the initial state of the molecule, we employ wavefunctions obtained through a Wannier orbital formalism that transforms the wavefunction of the whole liquid system into electronic orbitals localized over each water molecule in the liquid phase [1]. In particular, we consider coplanar geometries in which the incident, scattered and ejected electrons lie in the same plane. Moreover, we analyze asymmetric kinematic conditions for the scattered and ejected electrons (ejected energies of some eV). By means of an approximate static potential, we obtain an estimation of the influence of the passive electrons of the molecule (those not ionized) on the ionization process. We compute MDCS for the 1B 1 orbital of the water molecule as a function of the ejection angle at definite scattering angle, incident and ejected energies, and for fixed orientations of the molecule. It is observed that MDCS depend strongly on the orientation of the molecule. As experimental results of MDCS at fixed molecular orientations for liquid water are not available, we compare our theoretical predictions with other theoretical ones obtained for water molecules in gas phase [2]. In addition, as molecules are randomly oriented in experiments with water vapor [3], we also present MDCS averaged over all molecular orientations. The main physical features of the experiments (such as binary and recoil peaks) are similar to the ones observed in our results. Finally, we compare them with previous Fig 1. MDCS averaged over all molecular orientations. E i = 250 eV, E e = 10 eV and θ s =15º. Full line, present results for the liquid phase. Solid circles, experiments for the gas phase [3] conveniently normalized. Dashed line, previous caculations for the gas phase [4]. Dotted line, FBA-CW for the liquid phase [6]. Dash-dotted lines, FBA-CW for the gas phase [6]. theoretical predictions by other authors for gas phase [4] in which the bound state of the water molecule is described by means of single 68 Valparaíso, Chile
V Encuentro Sud Americano de Colisiones Inelásticas en la Materia centered Moccia's orbitals [5]. It is worthy to mention that this is the only difference in the theoretical treatment of both models. Also, we compare with recent calculations for both thermodynamical phases here analysed, obtained again within a similar theoretical framework but now with monocentric wavefunctions for the water molecule constructed by employing a Gaussian basis [6]. In Fig. 1, we present our theoretical MDCS averaged over all molecular orientations for an incident energy E i = 250 eV, ejected energy E e = 10 eV and scattering angle θ s =15º. We have conveniently normalized the experiments for the gas phase as they were obtained in a relative scale [3]. As can be seen, our results describe the characteristic two-lobe structure found in the experimental data for the binary region. Moreover, all the theoretical predictions considered in the figure present binary and recoil structures in qualitative good agreement. In particular, our predictions present a very good agreement with the theoretical calculation for the liquid phase of Ref. [6]. References [1] P. Hunt, M. Sprik and R. Vuilleumier, Chem. Phys. Lett. 376, 68 (2003). [2] C. Champion et al, Phys. Rev. A 63, 052720 (2001); C. Champion et al, Phys. Rev. A 72, 059906 (2005). [3] D. S. Milne et al, Phys. Rev. A 69, 032701 (2004). [4] C. Champion et al, Phys. Rev. A 73, 012717 (2006). [5] R. Moccia, J. Chem. Phys. 40 2186 (1964). [6] C. Champion, Phys. Med. Biol. 55, 11 (2010). 69 Valparaíso, Chile
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