Kinetic energies of fragment ions produced by electron impact on SF6

An apparatus has been constructed to study the kinetic energies of fragment ions SFn+ (n = 1-5) produced by electron impact on SF6 molecules. The retarding curves of the ions were produced by using a retarding field analyser of einzel lens type [1], and the second derivative method was employed to determine the maxima of the kinetic energy distribution curves. The SF5+ ions are formed primarily by predissociation of the ground or lower vibrational levels X∼, A∼ and B∼ of the parent ion. The kinetic energy of these ions is zero. The other channel of production is from dissociative ionization of the electronic state C∼ with a maximum of the kinetic energy distribution at 80 meV. The SF4+ , SF3+ , SF2+ and SF+ ions do not appear with zero kinetic energy, which indicates their formation either by preionization of super excited states of SF6 molecules (internal conversion with vibrational predissociation), or by predissociation processes through the repulsive branches of the parent ion electron states. (Author)