Numerical Green's functions in optical potential calculations for positron scattering from argon and neon

An optical potential method was applied to the calculation of positron scattering from the noble gases in order to determine the effect of open excitation channels on the shape of differential scattering cross sections

Quantum coherent control of the photo\-electron angular distribution in bichromatic ionization of atomic neon

We investigate the coherent control of the photo\-electron angular distribution in bichromatic atomic ionization. Neon is selected as target since it is one of the most popular systems in current gas-phase experiments with free-electron lasers (FELSs). In particular, we tackle practical questions, such as the role of the fine-structure splitting, the pulse length, and the intensity. Time-dependent and stationary perturbation theory are employed, and we also solve the time-dependent Schr\"odinger equation in a single-active electron model. We consider neon ionized by a FEL pulse whose fundamental frequency is in resonance with either $2p-3s$ or $2p-4s$ excitation. The contribution of the non\-resonant two-photon process and its potential constructive or destructive role for quantum coherent control is investigated.Comment: 10 pages, 6 figure

Close-Coupling and Distorted-Wave Calculations for Electron-Impact Excitation of the (5p⁵6p) States of Xenon

We report on a series of calculations for electron-impact excitation of the (5p56p) states in xenon from the ground state (5p6)1S0 . As in previous calculations for other noble-gas targets, we find strong evidence of channel coupling for all incident energies considered (between threshold and 200 eV ). Although qualitative agreement with the experimental results of Fons and Lin [Phys. Rev. A 58, 4603 (1998)] is achieved, severe quantitative discrepancies of sometimes more than a factor of 2 remain

Calculation of the polarization fraction and electron-impact excitation cross sectionfor the Cd+ (5 p) 2 P3/2 state

We present relativistic convergent close-coupling and Breit-Pauli R-matrix calculations for the polarization of the light emitted after electron-impact excitation of the (5s)2S1/2→(5p)2P3/2 transition in Cd+. While we find consistency between the theoretical predictions, a discrepancy persists with the measurements of Goto et al. [Phys. Rev. A 27, 1844 (1983)]. Cascade contributions and hyperfine depolarization effects were calculated and found to have negligible effect on the polarization fraction. We also present angle-integrated cross sections for the (5p)2P3/2 state to compare with the measurements of Gomonai [Optc. Spect. 94, 488 (2003)]. Agreement between theory and experiment is far from perfect, especially at low energies, where they disagree both in the absolute values and the energy dependence of the cross sections

Box-based and Laguerre-based convergent close-coupling calculations of electron–helium ionization

We apply a new implementation of the convergent close-coupling (CCC) method to electron–helium scattering. The target states are obtained from one-electron He+ box-based eigenstates rather than the usual Laguerre-based orbitals. The utility of the new method is demonstrated for 50 eV electron-impact ionization of helium with three different energy sharings between the two outgoing electrons. Excellent agreement is found between previous and new CCC predictions, and also with experimental data

Uncertainty Estimates for Theoretical Atomic and Molecular Data

Sources of uncertainty are reviewed for calculated atomic and molecular data that are important for plasma modeling: atomic and molecular structure and cross sections for electron-atom, electron-molecule, and heavy particle collisions. We concentrate on model uncertainties due to approximations to the fundamental many-body quantum mechanical equations and we aim to provide guidelines to estimate uncertainties as a routine part of computations of data for structure and scattering.Comment: 65 pages, 18 Figures, 3 Tables. J. Phys. D: Appl. Phys. Final accepted versio

Energy Dependence of the (\u3cem\u3ee\u3c/em\u3e,2\u3cem\u3ee\u3c/em\u3e) Recoil Peak to Binary Peak Ratio Across He (2\u3cem\u3ep\u3c/em\u3e\u3csup\u3e2\u3c/sup\u3e)\u3csup\u3e1\u3c/sup\u3e\u3cem\u3eD\u3c/em\u3e and (2\u3cem\u3es\u3c/em\u3e2\u3cem\u3ep\u3c/em\u3e)\u3csup\u3e1\u3c/sup\u3e\u3cem\u3eP\u3c/em\u3e Autoionizing Levels

The (e,2e) recoil peak to binary peak ratio as a function of the ejected-electron energy is reported for helium autoionizing levels (2p2)1D and (2s2p)1P. A special out-of-plane geometry is used where the ejected electrons are detected in a plane that includes the momentum transfer axis but is perpendicular to the scattering plane. The measured recoil peak to binary peak ratio is a dimensionless quantity that can be directly compared with calculations. A second-order model in the projectile-target interaction correctly reproduces the observed energy dependence and magnitude of the ratio, while a first-order model does not

Low and intermediate energy electron collisions with the C2−_2^- molecular anion

Calculations are presented which use the molecular R-matrix with pseudo-states (MRMPS) method to treat electron impact electron detachment and electronic excitation of the carbon dimer anion. Resonances are found above the ionisation threshold of C$_2^-$ with $^1\Sigma^+_g$, $^1\Pi_g$ and $^3\Pi_g$ symmetry. These are shape resonances trapped by the effect of an attractive polarisation potential competing with a repulsive Coulomb interaction. The $\Pi_g$ resonances are found to give structure in the detachment cross section similar to that observed experimentally. Both excitation and detachment cross sections are found to be dominated by large impact parameter collisions whose contribution is modelled using the Born approximation.Comment: 18 pages, 5 figures constructed from 8 file