Halogen Atom Abstraction Dynamics of Fluorine Atoms Reacting with Allyl Bromide and Iodobenzene Molecules

Article abstract of DOI:10.1021/j100093a019

Reactive scattering of F atoms with C3H5Br and C6H5I molecules leading to Br and I atom abstraction has been studied at an initial translational energy E ca. 40 kJ mol^-1 using a supersonic beam of F atoms seeded in He fuffer gas.The center-of-mass angular distributions of BrF and IF scattering show peaking in the forward and backward directions, which is consistent with reaction via persistent C3H5-Br-F and C6H5-I-F complexes with lifetimes greater than two rotational periods.The sharply peacked angular distribution observed for F + C3H5Br is consistent with a microcanonical description, whereby reactive scattering arises from a product transition state which approximates to a strongly prolate symmetric top.The mildly peaked angular distribution observed for F + C6H5I is consistent with a phase space description whereby unconstrained rotation is established between the nascent molecules in the product transition state.The product translational energy distributions are both consistent with randomization of energy over internal modes of the collision complex.The lifetime of the C3H5BrF collision complex greatly exceeds that of the FCH2-^.CH-CH2Br free radical intermediate in the Br atom displacement pathway, showing that these radicals are not coupled via a four-membered-ring transition state.Similarly, the rate of coupling to the ^.CH2-CHF-CH2Br radical must be slower than the rate of dissociation of the C3H5BrF radical, and the rate of migration of the F atom to the ? system of the very long-lived C6H5IF radical must also be slower than its rate of dissociation.