Cross sections for elastic scattering of electrons by CF_3Cl, CF_2Cl_2, and CFCl_3

摘要

Differential, integral, and momentum transfer cross sections have been determined for the elastic scattering of electrons from the molecules CF _3Cl, CF_2Cl_2, and CFCl_3.With the help of a crossed electron beam-molecular beam apparatus using the relative flow technique, the ratios of the elastic differential cross sections (DCSs) of CF_3Cl, CF_2Cl_2, and CFCl_3 to those of He were measured in the energy region from 1.5 to 100 eV and at scattering angles in the range 15° to 130°. From those ratios, the absolute DCSs were determined by utilizing the known DCS of He. For CF_3Cl and CF_2Cl_2, at the common energies of measurement, we find generally good agreement with the results from the independent experiments of Mann and Linder; J. Phys. B 25, 1621 (1992)10.1088/0953-4075/25/7/030; Mann and Linder J. Phys. B 25, 1633 (1992)10.1088/0953-4075/25/7/031. In addition, as a result of progressively substituting a Cl-atom, undulations in the angular distributions have been found to vary in a largely systematic manner in going from CF_4 to CF_3Cl to CF_2Cl_2 to CFCl_3 and to CCl_4. These observed features suggest that the elastic scattering process is, in an independently additive manner, dominated by the atomic-Cl atoms of the molecules. The present independent atom method calculation typically supports the experimental evidence, within the screened additivity rule formulation, for each species and for energies greater than about 10-20 eV. Integral elastic and momentum transfer cross sections were also derived from the measured DCSs, and are compared to the other available theoretical and experimental results. The elastic integral cross sections are also evaluated as a part of their contribution to the total cross section.