Virtual-state effects in electron scattering from HF molecules

Electron scattering by polar molecules in sub-milli-electronvolt energy region might be strongly affected by bound or virtual dipole-supported states. The position of the corresponding S-matrix poles in the complex energy plane depends on the total angular momentum J. For electron scattering by the HF molecule the author has a pure virtual state with the energy 1-1.5 meV at J=O. For higher J the pole moves off the real axis in the energy plane, or off the imaginary axis in the momentum plane. With growth of J the pole moves farther from the physical region and affects weaker the collisional cross sections. The author analyzes how the pole's position influences the elastic scattering and rotationally inelastic collisions in the energy range below 2 meV