Ultrafast capture of free electrons in optically ionized gases by the electron scavenger SF6

Time-resolved THz spectroscopy is applied to study directly the ultrafast free-electron dynamics in optically ionized gaseous Ar, SF6, and an Ar-SF6 mixture. The free-electron decay in the Ar plasma is accelerated enormously by adding small amounts of the electron scavenger SF6, which is assigned to resonant electron attachment.