Ionization in Rydberg-atom–SF6collisions at highn

Absolute rate constants for ionization of Rb(ns,nd) atoms in collisions with ${\mathrm{SF}}_6$ have been measured for values of n in the range 38–106. In addition, the kinematics of such reactions have been investigated using Xe(nf) atoms. The data confirm that collisions of Rydberg atoms with targets that attach free low-energy electrons are well described by the ‘‘essentially-free’’-electron model. Analysis of the data shows that the cross section σ(v) for electron attachment to ${\mathrm{SF}}_6$ at very low electron energies (≲10 meV) is inversely proportional to the electron velocity v and, if v is expressed in cm ${\sec }^{\mathrm{-}1}$, is given by σ(v)=(4.2±1.0)×${10}^{\mathrm{-}7}$/v ${\mathrm{cm}}^2$.