Thermionic electron emission from SF6-

L The rate coefficient for thermionic emission of SF6- is calculated from first principles, i.e., level densities of SF6 and SF6-, the known electron attachment cross section, and the principle of detailed balance. The decay of SF6- is calculated for different conditions in the SF6- formation process. It is demonstrated that a power law as well as exponential decays may be obtained depending on the experimental conditions in a measurement of the SF6- lifetime. The time dependence of the decay rate recently obtained at an electrostatic storage ring is accounted for by the obtained rate coefficient when the initial energy spread of SF6 and the kinetic energy of the free electron prior to attachment are included.