Differential cross sections (DCS) for the elastic scattering of electrons have been measured by the crossed-beam technique for CO, CO 2 , CH 4 , C 2 H 4 and C 2 H 6 in the angular range 30 • -120 • and at impact energies of 300, 500, 700, 900, 1100 and 1300 eV. The measurements were made with a view to test the validity of the independent atom model (IAM) for polyatomic molecules in this energy region. A comparison of experimental results with the IAM calculations indicates that the model is adequate for the linear molecules CO and CO 2 in the energy region 900-1300 eV. The Born approximation for the evaluation of the atomic scattering amplitudes was found to be valid only at 1300 eV for all the molecules except for C 2 H 6 . A survey of the previous experimental and theoretical data based on different models shows that proper molecular wavefunctions have to be used for the evaluation of short-range potentials and that valence-bond distortion, absorption and non-adiabatic effects in the polarization potential have to be considered.

With the help of Ge(Li)

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