Scattering of K atoms from oriented CF3I. Reaction at both “ends”

Abstract

The reaction of K atoms with CF₃I molecules has been studied using oriented molecules. If the I end is closest to the incoming K atoms, KI is formed and recoils backwards in the centre of mass system. If the CF₃ end is closest to the incoming K atoms, KI is again formed but scatters forwards in the CM. This is in contrast to the oriented CH₃I + Rb reaction in which no forward scattering is observed from configurations with CH₃ closest to the incoming Rb.

These observations find possible explanation in two (probably related) mechanisms. Even for CF₃I oriented in what appears to be an unfavorable configuration, it is possible for the K atom to fly past the CF₃ group and strike the I. This is expected to be less likely in CH₃I because the CH₃ shields the I more than does CF₃.

For CF₃I (but not CH₃I) charge transfer to a repulsive ionic state is postulated. The products are expected to recoil along the direction of the molecular axis and this roughly accounts for the experimental angular distribution.