Single electron ionization from H2O molecules by ion impact: a comparison between different approaches

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

Madrid

Workshop; Nano-IBCT Workshop "Quantum Scattering Codes and Monte-Carlo Simulations to Model Dynamical Processes in Biosystems"; 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 description of the initial bound and the final continuum states of the emitted electron. To this end, different approaches are employed, within the post and prior 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., each molecular orbital in the initial channel is written as a linear combination of atomic orbitals of the atomic constituents of the molecule. In a second approach, we employ the description given by Moccia 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. Also, an initial molecular three-centre wavefunction is considered, being this one obtained as a linear combination of Slater orbitals centred on each target nucleus. The final states are represented by a double product of projectile and target coulomb continuum factors with different effective target charges and a plane wave. These continuum states are chosen within a molecular three-effective centre approximation, obtained by extending the two-effective centre approximation. 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. In general, a reasonable agreement with experimental data is obtained. Differences can be observed between CNDO results obtained employing the post and the prior version of the transition amplitude, being the last one in better agreement with experiments for both backward and forward emission angles. Concerning the post version, it can be observed that three-ffective centre results present an enhancement at backward angles with respect to the CNDO and Moccia calculations, showing a better agreement with experimental data, in particular for the highest electron emission energies.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. Also, an initial molecular three-centre wavefunction is considered, being this one obtained as a linear combination of Slater orbitals centred on each target nucleus. The final states are represented by a double product of projectile and target coulomb continuum factors with different effective target charges and a plane wave. These continuum states are chosen within a molecular three-effective centre approximation, obtained by extending the two-effective centre approximation. 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. In general, a reasonable agreement with experimental data is obtained. Differences can be observed between CNDO results obtained employing the post and the prior version of the transition amplitude, being the last one in better agreement with experiments for both backward and forward emission angles. Concerning the post version, it can be observed that three-ffective centre results present an enhancement at backward angles with respect to the CNDO and Moccia calculations, showing a better agreement with experimental data, in particular for the highest electron emission energies.