Negative ion formation in halocarbons by charge exchange with cesium

Abstract

A crossed molecular beam apparatus is used to study the formation of anions by charge exchange of fast cesium atoms with a variety of halocarbons. The branching ratios are determined from threshold to 350 eV. Comparison of the spectator stripping and information theoretical models to the data leads to the conclusion that this class of reactions is an example of an ultradirect impulsive mechanism. In the most favorable case, that of CF3I, we have determined the near threshold relative cross sections for the anions CF3I−, I−, CF−3, and IF−. From these we determine the electron affinity of CF3I− to be 1.4±0.2 eV and the bond dissociation energy of CF3-I− as 0.38±0.1 eV, which disagrees with values obtained in a previous experiment.