Cross Sections for Electron Attachment Resonances Peaking at Subthermal Energies

Abstract

A simple procedure is described whereby both the magnitude and the energy dependence of the cross section for subthermal peaking electron attachment resonances are determined from electron swarm data alone. For an initial energy region it is shown that the attachment cross section can be approximated by σa(ε) = Aγ / εγ, and a determination of the power γ of the electron energy ε as well as of the corresponding constant Aγ yields both the magnitude and the energy dependence of the cross section at thermal and epithermal energies. The values of Aγ [in (ergs)γ square centimeters], γ, and σa(0.05 eV) (in square centimeters) are 2.5 × 10−29, 1.12, 1.17 × 10−14; 7 × 10−34, 1.412, 2.17 × 10−15; 9.1 × 10−32, 1.148, 1 × 10−16; and 1.66 × 10−29, 1.031, 5.2 × 10−16 for sulfur hexafluoride, 1,4-naphthoquinone, anthracene, and 1,2-benzanthracene, respectively. The thermal (T = 298°K) value of the attachment rate for SF6 in the carrier gases N2 and C2H4 is found to be 8.7 × 109 sec−1·torr−1 and 9 × 109 sec−1·torr−1, respectively. These values are in excellent agreement with the most reliable data available which are summarized. Cross sections are reported also for SF5− at 298°K. This work demonstrates further the potential of the electron swarm method in electron attachment studies.