Abstract
The two-centre wave-packet convergent close-coupling approach to ion–atom collisions is extended to study proton collisions with molecular hydrogen including electron-capture channels. We use a model potential to represent the molecular target as an effective one-electron spherically symmetric system. This greatly simplifies the target structure, allowing us to use already existing code developed for ion collisions with single-electron targets. Calculated total cross sections for electron capture, single ionisation, and excitation processes generally agree well with experimental data and other theoretical calculations where available. However, the total electron capture cross section is found to overestimate the experimental data at low energies, while the total ionisation cross section is slightly underestimated. Additionally, we present state-resolved cross sections for capture into the 1s, 2ell , and 3ell states of the projectile where deviation between various previous calculations is substantial. Our results lead to overall improvement over previous theoretical studies although discrepancies with experiment are observed for 3p and 3d capture. We conclude that treating molecular hydrogen as an effective one-electron system within the two-centre coupled-channel approach to one-electron targets can give reasonably accurate total cross sections at intermediate and high energies, without the need for a complex and computationally demanding two-electron target representation.
Highlights
The simplest homonuclear diatomic molecule is twoelectron molecular hydrogen
Elizaga et al [49] calculated electron-loss cross sections for proton scattering on H2 using a model potential representation in a molecular orbital (MO) treatment based on the optimised dynamical pseudostates (ODP) method and eikonal classical trajectory Monte Carlo (CTMC) approach
We use a two-centre expansion of the total scattering wave function in terms of target-centred and projectile-centred pseudostates and a plane wave representing the relative motion of the other particle, to allow us to differentiate between direct ionisation, electron capture, and electron capture into the continuum we can construct them by solving the radial Schrodinger equation with the model potential using an iterative Numerov approach
Summary
The simplest homonuclear diatomic molecule is twoelectron molecular hydrogen. The multicentre nature of H2 makes it difficult to accurately represent its structure, requiring complex theoretical descriptions and computationally demanding codes. One-centre close-coupling calculations using this approach to the target structure showed good agreement with experiment for ionisation in collisions with antiprotons [27] This technique was applied to positive projectiles to calculate total electron loss from 10 to 4000 keV and 2p excitation [48] (above 100 keV) cross sections for proton scattering on molecular hydrogen. Elizaga et al [49] calculated electron-loss cross sections for proton scattering on H2 using a model potential representation in a molecular orbital (MO) treatment based on the optimised dynamical pseudostates (ODP) method and eikonal classical trajectory Monte Carlo (CTMC) approach Their results agree closely with those of Luhr et al [48], except below 30 keV where the CTMC results underestimate both the experimental data [11] and the other calculations. Atomic units are used throughout this manuscript
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