Temperature Dependent Studies of Negative Ion Lifetimes

The lifetimes of $SF_6^- $ ions produced in K(\textit{np})/SF$_{6}$ collisions at high $n$ are being investigated as a function of target temperature over the range 300K to 600K. At room temperature, collisions are found to lead predominantly to the formation of long-lived $SF_6^- $ ions with lifetimes $\tau >$1ms. As the target temperature is raised long-lived ($\tau >$0.5ms) ions are still observed but their mean lifetime is reduced. In addition, the growth of a short-lived ion signal ($\tau <$10 $\mu $s) is evident which, by 600K, accounts for $\sim $45{\%} of the total $SF_6^- $ ion signal. These lifetimes are compared with those obtained using quasi-equilibrium theory and calculated $SF_6^- $ vibrational frequencies. Measurement and theory are being extended to other attaching targets to further examine the factors that govern negative ion lifetimes.