In this paper, we discuss the experimental technique for real-time measurement of the lifetimes of the collision complex of bimolecular reactions. An application to the atom-molecule Br + I, reaction at two collision energies is made. Building on our earlier Communication [J. Chem. Phys. 95, 7763 ( 1991)], we report on the observed transients and lifetimes for the collision complex, the nature of the transition state, and the dynamics near threshold. Classical trajectory calculations provide a framework for deriving the global nature of the reactive potential energy surface, and for discussing the real-time, scattering, and asymptotic (product-state distribution) aspects of the dynamics. These experimental and theoretical results are compared with the extensive array of kinetic, crossed beam, and theoretical studies found in the literature for halogen radical-halogen molecule exchange reactions.
Recently, we presented a formalism for extracting highly resolved spectral information and the potential of bound isolated systems from coherent ultrafast laser experiments, using I, as a model system [Gruebele et aZ., Chem. Phys. Lett. 166, 459 ( 1990)]. The key to this approach is the formation of coherent wave packets on the potential energy curve (or surface) of interest, and the measurement of their scalar and vector properties. Here we give a full account of the method by analyzing the coherences of the wave packet in the temporal transients of molecules excited by ultrashort laser pulses, either at room temperature, or in a molecular beam. From this, some general considerations for properly treating temporal data can be derived. We also present a direct inversion to the potential and quantum and classical calculations for comparison with the experiments.
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