Resonances in Electron Molecule Scattering: an Approach for their Identification and a Study of Dissociative Electron Attachment to H₂ and SO₂

Bingham, Peter Samuel (2024). Resonances in Electron Molecule Scattering: an Approach for their Identification and a Study of Dissociative Electron Attachment to H₂ and SO₂. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00095916

Abstract

This thesis investigates the role of resonances in electron-molecule scattering with a particular focus on their facilitation of dissociative electron attachment (DEA). It examines the resonances in electron scattering from H₂ and SO₂ and explores, both through application and implementation, methods for their identification and characterisation.

We present an implementation of a technique for the identification and characterisation of resonances based on the analytical continuation of the Jost function. Tests are carried out using analytical and molecular R-matrix data sets in order to investigate the strengths and limitations of the technique.

Scattering calculations are carried out for H₂ and SO₂ using the R-matrix method to allow: i) application of various existing techniques to identify and characterise the resonances in these systems; ii) identification of links from the resonances to DEA and other experimental works.

Velocity slice imaging (VSI) experiments of electron scattering from H₂ have revealed asymmetries in the momentum distributions of dissociated hydrogen anions at energies around 15 eV. In order to investigate this time-delays are used for the identification and characterisation of 35 resonances (∼ 30 are newly discovered) between bond lengths of 1.1 to 4.0 a₀ for energies from 12 to 15 eV. None of our calculated resonances could reproduce the asymmetries in the momentum distributions using a simple two resonance model provided in the literature.

For electron scattering from SO₂ there are inconsistencies between the resonances reported in the experimental and theoretical literature. To provide a more accurate and definitive description of the resonances time-delays and eigenphase sums are used for the identification and characterisation of six resonances at equilibrium geometry for energies up to 10 eV. A major finding is that even with 300 target states included in the calculation the results are not converged. Analysis shows our results are potentially compatible with experiment, although further work is still required.

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