Dipole and non-dipole excitation in collisions of low energy electrons with diatomic molecules

The authors have measured the rotational envelopes of selected vibrational bands of H2, D2, N2 and CO following excitation of cooled ( approximately 25K) gas beams. The observed broadening in N2 and CO at low impact energies is attributed to a breakdown of the electric dipole rotational selection rule mod Delta J mod =1. No broadening is observed in H2 or D2.