Trajectory Studies of Halogen Atom—Molecule Exchange Reactions

We studied the reactions $\mathrm{X}+{\mathrm{Y}}_2\to \mathrm{XY}+\mathrm{Y}$ , usually with X=Br, Y=I but with a few calculations for other choices (X=Cl or Y=Br). We used empirical potential surfaces having minima 0–10 kcal deep. In addition we could control all aspects of the shape and position of this potential well. Comparison with recent experimental results reveals that no reasonable potential well for collinear reactant approach will explain the observed scattering. The calculated behavior of the reaction is relatively insensitive to well properties, though it continues to depend on other potential shape parameters in the usual way. We suggest that the characteristic features of $\mathrm{X}+{\mathrm{Y}}_2$ reactive scattering may arise from the predominant effect of some feature of the interaction potential at fairly large reactant separation. Comparison of our results with those of trajectory studies for ${\mathrm{D}}^{+}+{\mathrm{H}}_2$ indicates that formation of a long‐lived intermediate complex in the neighborhood of a potential well will in practice depend sensitively on the particle masses and initial energies.