LOW-ENERGY SCATTERING IN H2, N2 AND 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, N2 and O2. 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 arc in good agreement, whereas for N2 experimental values of sigma(B) and SIGMA(M) conflict below 80 meV and agreement with theories is mixed. For O2, dicrepancies are greater than for N2 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.