Double differential cross sections for ionization of water molecules by ion impact

C. A. TACHINO; J. M. MONTI; O. A. FOJÓN; C. CHAMPION; R. D. RIVAROLA

Heidelberg

Congreso; 16th International Conference on the Physics of Highly Charged Ions; 2012

Single electron ionization from water molecules by impact of bare ions is studied. The aim of this work is to investigate the role played by the representation of the initial bound and the final continuum states of the emitted electron. To this end, two different approaches are employed, within the post version of the CDW-EIS (Continuum Distorted Wave-Eikonal Initial State) model. In the CNDO (Complete Neglect of Differential Orbitals) approximation proposed by Senger et al. [1], each molecular in the initial channel is written as a linear combination of atomic orbitals of the atomic constituents of the molecule. In the second approach we employ the description given by Moccia [2] for the ground state of AHn-type molecules, where the molecular orbital bound wavefunction is expressed as a weighted sum of Slater-type functions all centred in the heaviest nucleus of the target. The final states are represented by coulombic continuum ones with different effective target charges. Double differential cross sections (DDCS) as a function of the energy and angle of the emitted electron were calculated for impact of protons and C6+ ions on H2O molecules at intermediate and high collision energies. Differences can be observed between both set of theoretical data, being these discrepancies more pronounced in the case of C6+ ion impact. In general, a reasonable agreement with experimental data [3] is obtained. For forward emission angles, the DDCS calculated with CNDO are larger than the ones obtained with the Moccia representation, becoming these differences smaller as the energy of the emitted electron increases. For backward angles, the situation is reversed since the CNDO results are smaller than the Moccia ones. A prior version is also employed in order to study possible post-prior discrepancies in the CDW-EIS model. The importance of the dynamic screening produced by the residual electrons on the active one in the exit channel is studied. n-type molecules, where the molecular orbital bound wavefunction is expressed as a weighted sum of Slater-type functions all centred in the heaviest nucleus of the target. The final states are represented by coulombic continuum ones with different effective target charges. Double differential cross sections (DDCS) as a function of the energy and angle of the emitted electron were calculated for impact of protons and C6+ ions on H2O molecules at intermediate and high collision energies. Differences can be observed between both set of theoretical data, being these discrepancies more pronounced in the case of C6+ ion impact. In general, a reasonable agreement with experimental data [3] is obtained. For forward emission angles, the DDCS calculated with CNDO are larger than the ones obtained with the Moccia representation, becoming these differences smaller as the energy of the emitted electron increases. For backward angles, the situation is reversed since the CNDO results are smaller than the Moccia ones. A prior version is also employed in order to study possible post-prior discrepancies in the CDW-EIS model. The importance of the dynamic screening produced by the residual electrons on the active one in the exit channel is studied.