Negative ion molecule reactions of WF6: evidence for a pressure dependent branching ratio

Rate coefficients have been measured in a selected ion flow tube (SIFT) for reactions of several negative ions with WF6. With the exception of SF-5, all the reactant ions studied having an electron detachment energy less than 3.36 eV reacted rapidly by charge exchange. SF-5 transferred a fluoride ion producing WF-7. Ions with detachment energies greater than 3.36 eV associated rapidly with WF-6. Br-, with a detachment energy of 3.36 eV, reacted with WF6 both by ion-neutral association and by charge exchange. The branching ratio for these two channels was found to depend on temperature and pressure. All these data indicate that the electron affinity of WF6 is nearly equal to that of Br