Branching ratios in reactive collisions: theory versus experiment

Recent experimental and theoretical studies of branching ratios in elementary bimolecular reactions are reviewed. Examples include both direct- and complex-mode reactions of neutral reagents yielding alternative sets of products (neutral or ionic as the case may be). The information-theoretic approach to branching ratios (and intramolecular isotope effects) for direct, exoergic reasons is illustrated. Recent molecular beam experiments on the energy dependence of the branching ratio for the decay of alkali halide--alkali collision complexes are discussed