Formation of SF5− in electron attachment to SF6; swarm and beam results reconciled

Based on the results of recent swarm experiments, it has been proposed that the increase in the cross section for SF5− formation observed at an electron energy, Ee of about 0.3 eV in electron beam studies of electron attachment to SF6 is due to the combined (opposing) effects of the vibrational heating of the molecule by the attached electron, which enhances the dissociation of the nascent (SF6−)∗ ion, and the reduction of the cross section for capture (s-wave) of the electron by SF6 with increasing Ee. Further, it has been shown that the dissociation reaction is endothermic by 0.12 eV, and that, contrary to previous suggestions, there is no potential barrier to this dissociation reaction. Now we have carried out electron beam studies of the SF6 attachment reaction in Berlin at gas temperatures, Tg, over the range 300 to 920 K and in Innsbruck at Tg below 300 K. These studies have provided support for the above proposals concerning the appearance of the SF5− peak and for a reaction endothermicity of 0.12 eV. Thus these studies have clarified the doubts about the products of the SF6 attachment reaction at low electron energy.