Negative ion production in collisions between K(n d) Rydberg atoms and CF3Br and CF2Br2

Negative ion production via electron transfer in collisions between K(nd) Rydberg atoms and CF3Br and CF2Br2 has been investigated over a wide range of of n (10≤n≤70). For both species, the major negative ion observed is Br−, although with CF2Br2, a small Br−2 signal is also detected. Kinematic studies show that Br− production via dissociative attachment is accompanied by sizable translational energy release (∼0.35 eV for CF3Br; ∼0.2 eV for CF2Br2). These studies further show that, despite this large energy release, post-attachment interactions between the product ions are important at intermediate values of n(n≲20) and suggest that the transient CF3Br−* and CF2Br2−* ions initially formed by electron capture have quite different lifetimes against dissociation. Cross sections for free-electron attachment to both species are derived from measurements of rate constants for electron transfer at high n. These cross sections are in reasonable agreement with results obtained in free-electron studies using the threshold photoelectron spectroscopy technique.