Dramatic steric behavior in electron transfer from various donors to CF3Br

Different alkali metal atoms are observed to donate electrons to CF3Br molecules that are oriented in space. For collision energies high enough to overcome the Coulomb attraction, a positive ion/negative ion pair is observed and mass-analyzed using coincident time-of-flight mass spectroscopy. The alkali metal cation and various negative ions are observed. The most abundant negative ion is the bromide ion, Br-, formed preferentially by attack at the Br end of the molecule. The steric asymmetry to produce Br- is almost identical for all of the alkali metal donors. Fluoride ions are formed in smaller abundance and reflect completely different behavior among the donors. Sodium and potassium have high thresholds and prefer the CF3 end of the molecule, whereas cesium prefers the Br end of the molecule. Sodium and potassium apparently interact with the transient CF3Br- molecular negative ion while it is in the process of decomposing.