Exchange effects in the rotational excitation of molecular hydrogen by slow electrons

The scattering formalism of Arthurs & Dalgarno (1960) is generalized to take account of exchange (but not polarization) in the scattering of slow electrons by molecular hydrogen. The use of a single-centre molecular wavefunction is discussed, and representative calcula­tions of the j = 0→ j = 2 rotational excitation cross-section are carried out in the distorted wave approximation. The inclusion of exchange results in a significant increase (rising from 12% at 0.1 eV to over 70% at 0.5 eV) in the dominant (p-wave) contribution to the cross-section. It is concluded that exchange effects cannot be ignored in the theoretical discussion of electron energy loss by rotational excitation in swarm experiments.