Semiclassical model for calculating fully differential ionization cross sections of the H2_2 molecule

Fully differential cross sections are calculated for the ionization of H$_2$ by fast charged projectiles using a semiclassical model developed previously for the ionization of atoms. The method is tested in case of 4 keV electron and 6 MeV proton projectiles. The obtained results show good agreement with the available experimental data. Interference effects due to the two-center character of the target are also observed and analyzed.Comment: 11 pages, 4 figure

Model potentials in liquid water ionization by fast electron impact

International audienceWe study the ionization of water molecules in liquid phase by fast electron impact. We use our previous first-order model within an independent electron approximation that allows the reduction of the multielectronic problem into a monoelectronic one. The initial molecular states of the liquid water are represented in a realistic way through a Wannier orbital formalism. We complete our previous study by taking into account approximately the influence of the passive electrons of the target by means of different model potentials. We compute multiple differential cross sections for the most external orbital 1B1 and compare them with other results

Double differential cross sections for liquid water ionization by impact of fast electrons

International audienceA theoretical study for the single ionization of water molecules in liquid phase by electron impact at high energies is presented. Through a first order model, we compute multiple differential cross sections considering an asymmetric coplanar geometry. The wavefunctions for a single liquid water molecule are obtained in a realistic way by using a Wannier orbital formalism. We compare our results with experiments for the vapor phase and previous theoretical results obtaining a good qualitative agreement

Theoretical study of the ionization of liquid water from its several initial orbitals by fast electron impact

International audienceWe theoretically study the single ionization of liquid water by energetic electrons through one active-electron first-order model. We analyze the angular ejected electron spectra corresponding to the most external orbitals 1B1, 2A1, 1B2 and 1A1 of a single water molecule. We work to create a realistic description of those orbitals corresponding to single molecules in the liquid phase. This goal is achieved by means of a Wannier orbital formalism. Multiple differential cross sections are computed and compared with previous calculations for both liquid and gas phases. In addition, our present results are integrated over all orientations and compared with experimental ones for randomly oriented vapour water molecules, as no experiments currently exist for the liquid phase. Moreover, we estimate the influence of the passive electrons on the reaction by means of a model potential

A multi-scale ab initio theoretical study of the production of free radicals in swift ion tracks in liquid water

International audienceUsing a multi-scale theoretical approach from first principles, we show that the production of HO2 radicals in liquid water can be understood from the initial Coulomb explosion of doubly ionized water molecules. Based on the separation of time scales, we used three different theoretical models, each one associated with a specific time scale. The initial ~1 fs of water radiolysis is taken care of with a Monte Carlo code whose basic ingredients are cross-sections. These have been calculated in the present work using the continuum distorted wave eikonal initial state (CDW-EIS) model framework. Our calculated cross-sections nicely demonstrate that double ionization of water molecules is one major event compatible with the experimental HO2 molecular rate production. The subsequent tens of fs following the double ionization of one water molecule of the liquid medium have been described with microscopic ab initio Car–Parrinello molecular dynamics simulations. Dynamics shows that the water Coulomb explosion leads to the formation of two H3O+ ions and an atomic oxygen atom. The final stage of the Coulomb explosion (up to the ms timescale) has been modelled with a chemical Monte Carlo code, assessing that the production of HO2 results from the O + OH → HO2 reaction in the liquid phase

Coherent electron emission from O

Absolute double differential cross sections (DDCS) of secondary electrons emitted in ionization of O2 by fast electrons have been measured for different emission angles. Theoretical calculations of atomic DDCS were obtained using the first Born approximation with an asymptotic charge of ZT = 1. The measured molecular DDCS were divided by twice the theoretical atomic DDCS to detect the presence of interference effects which was the aim of the experiment. The experimental to theoretical DDCS ratios showed clear signature of first order interference oscillation for all emission angles. The ratios were fitted by a first order Cohen-Fano type model. The variation of the oscillation amplitudes as a function of the electron emission angle showed a parabolic behaviour which goes through a minimum at 90°. The single differential and total ionization cross sections have also been deduced, besides the KLL Auger cross sections. In order to make a comparative study, we have discussed these results along with our recent experimental data obtained for N2 molecule

Ionization of N2 in collisions with fast electrons: Evidence of an interference effect

p { margin-bottom: 2.47mm; line-height: 120%; }Absolutedouble differential cross sections (DDCS) of electron emission weremeasured for ionization of N2 by fast electrons with energy 7 keV. Measurements wereperformed for different electron emission angles and energies.Evidence of oscillation due to Young-type interference was observedin the DDCS ratios for all angles. The frequency for large backwardangle is found to be larger compared to that for small forward angle.Consequently, the forward-backward asymmetry parameter reveals theoscillatory structure even more clearly. The oscillations observedfor both experimental-to-heoretical DDCS ratios and forward-backwardasymmetry were well explained by the Cohen-Fano model of interferencein a molecular double slit. A periodic deviation of the Cohen-Fanomodel from the asymmetry parameter data reveals the presence of ahigher-frequency component.The first Born model was employed to explain the results of molecularnitrogen for which a complete-neglect-of-differential-overlapapproximation was used along with an effective atomic number.Fil: Roy Chowdhury, Madhusree. Tata Institute of Fundamental Research; IndiaFil: Stia, Carlos Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Tachino, Carmen Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Fojon, Omar Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rivarola, Roberto Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Tribedi, Lokesh C.. Tata Institute of Fundamental Research; Indi