Exothermic gas phase electron transfer reactions: A+B=A+B, where A and B are polyatomic molecules with positive electron affinities, generally proceed at collision rates. However, reactions involving A=SF6 or perfluorocycloalkanes have rates which decrease with the exothermicity of the reaction, becoming very slow at low exothermicity. Earlier work attributed this behavior to the presence of an energy barrier, due to a large geometry change for A to A. The reaction coordinate used also involves the bond energies A ⋅ B and A ⋅ B. These were measured in the present work. It was found that the bond energy in SF6 ⋅ B is much larger than in SF6 ⋅ B . This difference increases the energy barrier very significantly and is thus an additional cause for the slow electron transfer. The bond energies for several other complexes like: Cl ⋅ B, Cl ⋅ SF6, Cl ⋅ perfluorocyloalkanes, and Cl ⋅ C6F6 were measured. These provide insights into the nature of the bonding involved. The work was performed with a pulsed electron high pressure mass spectrometer.

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