Formation of Heavy Rydberg K$^{+}-\mbox{SF}_6^- $ Ion-Pair States in K($n$p)-SF$_{6}$ Collisions

At low $n$ ($n\approx $10 -- 15), electron transfer in collisions between K($n$p) Rydberg atoms and SF$_{6}$ can lead to formation of bound K$^{+}-\mbox{SF}_6^- $ ion pairs that orbit at relatively large separations, frequently referred to as heavy-Rydberg ion-pair states because of their similarities to atomic Rydberg states. The production of such ion pairs is examined through measurements at different values of $n$ and with different Rydberg atom velocities. The lifetimes of the ion pairs are measured by observing the time development of the $\mbox{SF}_6^- $ signal, part of which results from dissociation of bound ion pairs through the transfer of internal energy from the $\mbox{SF}_6^- $ ions into translational energy of the ion pair. The data point to bound ion-pair lifetimes of $\sim $1 -- 2$\mu $s, which are many times larger than their orbital periods of $\sim $30 -- 150ps. This work is being extended to other attaching molecules to further examine the properties of heavy Rydberg systems.