Absolute elastic differential cross sections for electron scattering by C6 H5 CH3 and C6 H5 CF3 at 1.5-200 eV: A comparative experimental and theoretical study with C6 H6

We present absolute differential cross sections (DCS) for elastic scattering from two benzene derivatives C6 H5 CH3 and C6 H5 CF3. The crossed-beam method was used in conjunction with the relative flow technique using helium as the reference gas to obtain absolute values. Measurements were carried out for scattering angles 15°-130° and impact energies 1.5-200 eV. DCS results for these two molecules were compared to those of C6 H6 from our previous study. We found that (1) these three molecules have DCS with very similar magnitudes and shapes over the energy range 1.5-200 eV, although DCS for C6 H5 CF3 increase steeply toward lower scattering angles due to the dipole moment induced long-range interaction at 1.5 and 4.5 eV, and (2) that the molecular structure of the benzene ring significantly determines the collision dynamics. From the measured DCS, elastic integral cross sections have been calculated. Furthermore, by employing a corrected form of the independent-atom method known as the screen corrected additive rule, DCS calculations have been carried out without any empirical parameter fittings, i.e., in an ab initio nature. Results show that the calculated DCS are in excellent agreement with the experimental values at 50, 100, and 200 eV.