Rotational resonances in low-energy electron scattering by H2 and D2

The conditions necessary to sustain rotational resonances in very low-energy electron scattering by molecular hydrogen are examined. Semiempirical interaction potentials are used in close-coupling calculations to obtain resonance energies, as eigenvalues of a projected Hamiltonian, and phase shifts and resonance widths from solutions for the total Hamiltonian. An unrealistic electron-molecule interaction potential is required in order to sustain a rotational resonance under single collision conditions. However, at high densities where average molecular separations are of the order of 15a0 to 30a0, resonance structure can be generated through a model potential which includes a modification due to neighboring molecules. Effects due to the presence of molecular dimers are also investigated