Ionization Cross Sections of F2 and Cl2 by Electron Impact

Abstract

A measurement has been made of the electron impact ionization cross section of F₂ and Cl₂ over the energy range 15–100 V. Both species exhibit a maximum cross section at electron energies near 100 eV, the maximum values being approximately ${\text{1.5× 10}}^{\text{−16}}$ and ${\text{7.0× 10}}^{\text{−16}}\hspace{0.17em}{\mathrm{cm}}^2$ for F₂ and Cl₂, respectively. The measurement in Cl₂ fits an observed correlation between the maximum cross section and the square root of the polarizability. This correlation seems to apply to a wide variety of atomic and molecular species. Based on this correlation we estimate the polarizability of F₂ to be approximately ${\text{8× 10}}^{\text{−25}}\hspace{0.17em}{\mathrm{cm}}^3$