Molecular beam experiments show that diatomic molecule exchange reactions involving an ionic bond proceed readily at thermal collision energies. Previous work found two such reaction families, alkali halide + alkali halide and dialkali + halogen. This study adds a third, alkali halide + halogen. For CsI + Cl2→ CsCl + ICl the product angular and velocity distributions indicate that a statistical collision complex is formed which persists for many vibrational periods and at least a few rotational periods. This complex presumably corresponds to the alkali trihalide salt, Cs+(ClICl)–. For the CsBr + ICl reaction only formation of CsCl + IBr has been observed, even at collision energies well above the endoergic threshold for formation of CsI + BrCl. The energy disposal is not statistical and the product angular distribution is quite asymmetric about 90°, indicating that a large fraction ([graphic omitted] ⅓ to ½) of the collision complexes break up in less than one rotational period. The preferred directions of emission are 0° for CsCl and 180° for IBr, where 0° and 180° designate the incident beam directions (c.m. system) for ICl and CsBr, respectively. These properties can be plausibly interpreted in terms of the electronic structure of the trihalide group.