Thermal energy electron attachment rate constants for some polyatomic molecules

Abstract

Rate constants for the attachment of thermal energy electrons to a number of polyatomic molecules are reported. The attachment rate constants αw are determined in an electron swarm experiment under zero electric field conditions where the electrons have a Maxwellian energy distribution corresponding to the temperature of the nonattaching diluent gas. Various diluent gases were used, and no significant differences in the attachment rate constants were found. Corrections to the attachment rate constant measurements due to electron diffusion are small and are taken into account. Thermal energy attachment rate constants are reported for the following molecules (attachment rate constants are given in parentheses in units of cubic centimeters per second): SeF6(1.27 × 10−9), CCl4 (3.55 × 10−7) C7F14(4.0 × 10−8), C6F6(1.06 × 10−7), C7F8(2.42 × 10−7), C6F10(3.13 × 10−7), C5F8 (1.18 × 10−7), C4F8(1.11 × 10−8), C8H8(7.7 × 10−10), and SO2F2(5.8 × 10−10). Upper limits to the attachment rates for the following molecules were obtained using pure gases: CF4, C2F6, C3F8, CClF3, CHF3, CHClF2, C2H2F2, C2H4F2, C2ClF5, and TeF6. An upper limit of ∼3 × 10−12 cm3/sec for the thermal electron attachment rate constant for HC1 in a mixture with N2 as a carrier gas is reported and is more than 100 times smaller than a previously reported value.