Electronic and vibrational close-coupling method for resonant electron-molecule scattering*

In the field of electron-molecule scattering, direct and resonant scattering processes are treated using entirely separate theories. Close-coupling techniques such as molecular convergent close-coupling (MCCC) or R-matrix have had considerable success in studies of direct scattering, by applying the Born-Oppenheimer approximation to allow the electronic and nuclear motions to be decoupled. On the other hand, studies of resonant scattering typically decouple the direct and resonant scattering channels, solving the nuclear dynamics problem for the resonant processes with electronic resonance energies and widths taken from separate electronic scattering methods. We have now extended the MCCC method to include both electronic and vibrational states in the close-coupling expansion, allowing calculations to be performed in which direct and resonant scattering are coupled and treated on the same footing. We have applied the new technique to electron scattering on H2, and studied the resonance structures present in both elastic and excitation cross sections.