Transition state dynamics of F + Br2 reactive scattering

Abstract

Reactive scattering of F atoms with Br2 molecules has been studied at an initial translational energy E ∼ 16 kJ mol−1 using a supersonic beam of F atoms seeded in Ne buffer gas. Laboratory angular and velocity distributions of BrF product have been measured. They show sharp peaking in the forward direction with almost isotropic wide angle scattering of relative intensity ∼ 0.2. Approximately half the total available energy is disposed into product translation for scattering in the forward and backward directions with slightly lower translational energy for the sideways scattering. The combination of sharp forward scattering and high product translational energy is attributed to early migratory trajectories in large impact parameter collisions whereby the F atom reacts with the more distant Br atom of the Br2 molecule lying in the forward hemisphere. The isotropic wide angle scattering arises from direct trajectories in which the F atom reacts with the nearer Br atom of the Br2 molecule. Migratory dynamics are promoted by charge transfer interaction of the form Br2+F− which stabilises the potential energy surface in elongated isosceles triangular FBr2 configurations as well as in slightly bent FBrBr configurations. Comparison is made with the dynamics of the F + Cl2, I2, and CCl3Br reactions.