Electronic and vibrational close-coupling treatment of low-energy electron-H₂ scattering: Vibrational excitation and perspectives for dissociative attachment

Over the last few years, progress has been underway to incorporate the vibrational degree of freedom into the coupled-channels expansion of the scattering wavefunction in the molecular convergent close-coupling (MCCC) method. Typically, electron-molecule scattering theories apply various decoupling approximations to make the calculations tractable, e.g. decoupling the electronic and nuclear degrees of freedom (adiabatic-nuclei approximation), or decoupling the direct and resonant scattering processes. Here we will present results for low-energy vibrational excitation of H₂ by electron impact, demonstrating the feasibilty of taking the electronic and vibrational close-coupling expansion to convergence in one of the most challenging cases where coupling to a large number of closed electronic states plays an important role in describing target polarisation. We will make comparisons with the adiabatic and resonance-theory approximations, drawing conclusions about the strengths and weaknesses of both. We will also discuss some interesting connections the present calculations have to the description of positronium formation in positron-atom and -molecule scattering, which will guide our next steps in incorporating dissociative attachment.