Ionization cross sections of F2 and Cl2 by electron impact

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 1.5× 10−16 and 7.0× 10−16 cm2 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 8× 10−25 cm3