Transition state dynamics of F + ICl, C₂H₅I reactive scattering

Abstract

Reactive scattering of F atoms with ICl and C₂H₅I molecules has been studied at an initial translational energy E ∼ 12 kJ mol^-1 using a supersonic beam of F atoms seeded in Ne buffer gas. The centre-of-mass angular distribution of IF scattering for F + ICl, measured previously at E ∼ 34 kJ mol^-1, shows peaking mainly in the forward direction, which is consistent with reaction via a short-lived complex with a lifetime of half a rotational period. The microcanonical theory for dissociation of a persistent complex via a prolate symmetric top transition state accounts for the higher energy F + ICl scattering arising from the full range of impact parameters. The angular distribution for F + C₂H₅I shows peaking in the forward and backward directions which is consistent with a complex lifetime greater than one rotational period. The extended microcanonical theory accounts for scattering by a range of transition state configurations generated by internal rotation about the extended C-I bond for collisions at the largest impact parameters together with a phase space description of scattering at smaller impact parameters. The angular distribution for F + ICl at E ∼ 12 kJ mol^-1 exhibits only mild peaking in the forward direction and a phase space description suffices for scattering from the full range of impact parameters. The strong dependence of the F + ICl reactive scattering on initial translational energy may be attributed to a contribution from migratory trajectories where the F atom interacts initially with the Cl atom of ICl. Nonmigratory trajectories involve the F atom interacting only with the I atom throughout, as in the F + C₂H₅I reaction.