Crossed molecular beam metathesis: Alkaline earth dihalides+Cl2 and HCl

Exploratory crossed molecular beam studies of bimolecular reactions of alkaline earth dihalides with halogen containing compounds are reported. The c.m. product distribution is symmetric about ϑ=90° for the BaI2+Cl2 halogen‐exchange reaction indicating formation of a collision complex which persists for a least a few rotational periods. The data are consistent with, but do not establish, formation of a similar complex in the SrI2+Cl2 reaction and with a statistical loose transition state energy partitioning in both reactions. The BaI2+HCl→BaICl+HI reaction is direct, favoring backscattering of the metal atom. Relative total reaction cross sections for the MX2+Cl2 halogen‐exchange reactions decrease as 1.0:0.45:<0.007 when M is varied from Ba to Sr to Mg. All of these observations support an ion‐pair adduct model which was previously advanced to interpret facile four‐center exchange reactions of cesium halides with diatomic halogens. This model, which qualitatively correlated observed trends with reactant ...