Convergent-close-coupling formalism for positron scattering from molecules

The ab initio convergent-close-coupling method has been extended to positron-molecule collisions within the adiabatic (fixed-nuclei) approximation. Application to molecular hydrogen at energies from 0.1 to 1000 eV has yielded convergent total ionization and grand total cross sections over most of the energy range. We find that very large calculations are required for convergence, even in the case of low-energy elastic scattering, due to the effects of positronium formation. In general, the comparison with experiment is good

Calculations of electron and positron scattering from vibrationally excited H2+ and H2

© Published under licence by IOP Publishing Ltd. Electron and positron scattering from the vibrationally excited H2 + and H2 molecules were investigated using the adiabatic-nuclei convergent close-coupling method. Converged results are presented for a range of vibrationally excited states

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

Electron-impact dissociation of vibrationally-excited molecular hydrogen into neutral fragments

We present convergent close-coupling (CCC) calculations of electron-impact dissociation of vibrationally-excited molecular hydrogen into neutral fragments. This work follows from our previous results for dissociation of molecular hydrogen in the ground vibrational level [Scarlett et al., Eur. Phys. J. D 72, 34 (2018)], which were obtained from calculations performed in a spherical coordinate system. The present calculations, performed utilizing a spheroidal formulation of the molecular CCC method, reproduce the previous dissociation cross sections for the ground vibrational level, while allowing the extension to scattering on excited levels

Double-K-vacancy states in electron-impact single ionization of metastable two-electron N5+(1s2s 3S1) ions

The role of hollow states intermediately produced in electron-impact ionization of metastable He-like N5+(1s2s3S1) ions has been investigated in detail. A crossed-beam setup and suitable experimental techniques were employed for the measurement of accurate absolute cross sections and precise energy-scan data. Fine structures arising from K-shell excitations and associated resonances have been observed for this two-electron ion with less than ±0.5 eV uncertainty on the energy scale. Fine details, such as interference of the reaction pathways of direct ionization and excitation with capture of the incident electron followed by double-Auger decay, could be revealed. Ab initio calculations based on the convergent close coupling (CCC) approach are in good agreement with the experiment

Electron scattering from molecular hydrogen in a spheroidal convergent close-coupling formalism

Electron scattering from molecules is a fundamental interaction of matter and is the mechanism behind many chemical reactions. In this work we rework the ab initio Convergent Close-Coupling scattering theory into prolate spheroidal coordinates–a natural system for diatomic molecules–to present total, differential, and ionisation cross sections of electron-H2 collisions

Accurate stopping power calculations for antiprotons and protons

© Published under licence by IOP Publishing Ltd. The convergent close-coupling method is applied to calculate antiproton and proton stopping cross sections for atomic and molecular targets. Excellent agreement with experimental measurements is obtained for antiprotons in helium while unexpectedly large disagreement is found for the hydrogen molecule, which is inconsistent with very good agreement between our ionisation cross section and the experiment

Photoionization from the ground and excited vibrational states of H+2 and its deuterated isotopologues

Photoionization cross sections and rate coefficients have been calculated for all bound vibrational levels of the 1s$\sigma_{\mathrm{g}}$ state of H$_{2}^{+}$, HD$^{+}$, and D$_{2}^{+}$. The Born-Oppenheimer approximation is employed in our calculation of vibrationally-resolved photoionization cross sections. Vibrationally-resolved and local thermal equilibrium photoionization rate coefficients are presented for photon temperatures less than $50\,000$ K and are found to be several orders of magnitude larger than previous results in the literature. Analytic fits for the vibrationally-resolved and local thermal equilibrium photoionization rate coefficients are provided. Near threshold oscillations in the vibrationall-resolved photoionization are observed. A benchmark set of photoionization cross sections are presented. Fixed-nuclei photoionization cross sections are calculated using two-center true continuum wave functions and are verified by comparison with previous calculations and are found to be in excellent agreement in all cases. Data files for our set of benchmark cross sections, rate coefficients, and fitting parameters for H$_{2}^{+}$, HD$^{+}$, and D$_{2}^{+}$ are available on Zenodo under an open-source Creative Commons Attribution license: https://doi.org/10.5281/zenodo.8304060 .Comment: Accepted in ApJ