Vibrational autodetachment of sulfur hexafluoride anions at its long-lifetime limit

Abstract

We have investigated the autodetachment of electrons from rovibrationally hot SF${}_{6}{}^{\ensuremath{-}}$ anions using a cryogenic ion-beam trap. Extremely low residual gas densities of ${10}^{4}$ cm${}^{\ensuremath{-}3}$ provided undisturbed observation of the neutralization rates due to vibrational autodetachment (VAD) over almost five orders of magnitude and over times up to 100 ms. We successfully explain our experimental decay curves using statistical rate theory combined with electron attachment data and vibrational frequencies calculated for a ${C}_{4v}$-distorted SF${}_{6}{}^{\ensuremath{-}}$. The unprecedented sensitivity of the experiment to the decay constants at the VAD threshold allows us to infer from the data the adiabatic electron affinity of SF${}_{6}$ to be $(0.91\ifmmode\pm\else\textpm\fi{}0.07)$ eV and to confirm the recently predicted ${C}_{4v}$ symmetry of SF${}_{6}{}^{\ensuremath{-}}$.