Low energy electron scattering in H2, N2and O2

Electron beam transmission experiments have been performed, in the energy range 10 meV to 175 meV, with a magnetically collimated electron beam formed in a synchrotron radiation photoionization source using SuperACO, LURE. The apparatus has been calibrated with He and absolute backward scattering cross sections have been measured for the target gases H 2 , N 2 and O 2 . A relationship, involving s and p partial waves, has been established between the backward scattering cross sections ( sigma B ) and the momentum transfer cross sections ( sigma M ). This has been used to check the accuracy of experimental data and the consistency of values of sigma B , sigma M and total scattering cross sections. Experimental data and theory for H 2 are in good agreement, whereas for N 2 experimental values of sigma B and sigma M conflict below 80 meV and agreement with theories is mixed. For O 2 , discrepancies are greater than for N 2 both in experimental data and between theory and experiment, which may differ by up to a factor of 5 for the total scattering cross section at the lowest energies.