Temperature dependence of electron attachment at low energies for polyatomic molecules

摘要

The cross sections for production of negative ions by attachment of lowhyphen;energy (0.2 eV) electrons to selected polyatomic (SF6, CCl4, CFCl3, CH2Br2, CH3I, CHCl3, CF3Br, CH3Br) molecules have been determined as a function of target gas temperature in the range from 300 to 1200deg;K. For the case of SF6it is found that thetotalcross section for negative ion production is independent of gas temperature, although it is known from the experiments of Chen and Chantry that the relative abundances of different species of negative ions produced from SF6are strongly temperature dependent. In contrast to SF6, the total cross sections for negative ion production in some halogenated hydrocarbons are found to be strongly temperature dependent. It is found that the total cross section for negative ion production in many polyatomic molecules tends towards an absolute maximum as the gas temperature is increased.