Dynamics of reactions between two closed-shell molecules

Abstract

The crossed molecular beam technique has been utilized to investigate a large number of elementary reactions. However, most of the studied reactions involve atoms or radicals; reactions between two stable molecular reactants are, in fact, seldom studied with the crossed molecular beam method. In this perspective, reactions between two stable molecules are reviewed and discussed. With crossed molecular beams and vacuum UV photoionization, the nascent products have been unambiguously identified. Consistent pictures of the reaction paths have been constructed based on the experimental data and ab initio calculations. Furthermore, there are intriguing features about the reaction barriers. The F₂ + organosulfur reactions are barrierless, demonstrating the first examples of such interactions between two closed-shell reactants. The barrier of F₂ + alkene reaction decreases with more methyl substitution groups at the CC double bond, yet the absolute barrier heights from experiment and theory disagree with each other by ∼2 kcal mol⁻¹, leaving an issue to be resolved in the future.