Harpoon clusters

The results, which are detailed elsewhere, reveal that the transition state of CT reactions can be studied directly at well-defined impact geometries. The dissociative CT reaction of benzenes with iodine occurs with an elementary harpoon/electron transfer mechanism. The time scales for the CT and for the product (I) formation define the degree of concertedness and, as reported elsewhere, are significant to the recent elegant studies in condensed media by Wiersma and colleagues and by Sension. So far we have studied the electron donors of benzene, toluene, xylene, mesitylene, and cyclohexane and we plan extension to other systems. We have also studied the effect of solvation in clusters and in solutions. 

The difference may arise from the radical character of the monomers versus the closed-shell electronic structure of the dimer Nj O4. In the former, because of the high electron afhnity, a harpooning process is expected, while in the dimers the interaction is short range with covalent character. It is important to realize that for collision energies of more than 10.5 kcal the cross section for the N2O4 reaction exceeds that of the monomeric process. It is difficult to conclude on the third-body effect in this reaction because of the differences in the electronic structure between the two species NO2 and N2O4. Usually one would like to investigate the cluster s effect where only small perturbations exist. 

Reactions of this type are, for example, initiated in van der Waals clusters, M---XR (M = alkali metal X = F, Cl, Br R = H,CH3,Ph), by absorption of visible light. This approach has allowed the study of the classic alkali-metal atom harpooning reactions. The metal atom M acts as the chromophore and, thereafter, charge transfer to the halide molecule XR results in dissociation of the complex, i.e. 

Farmanara P, Stert V, Radloff W, Skowronek S, Gonzalez-Urena A. 1999. Ultra-fast dynamics and energetics of the intra-cluster harpooning reaction in Ba FCH3 . Chem. Phys. Lett. 304(3-4) 127-133. 

The cover illustration is by the late Israeli physical chemist and artist Jacob Wilf. Jacob was my friend and we had many scientific discussions. One result is that he has drawn several paintings depicting themes from Molecular Reaction Dynamics such as harpoon reactions, stereodynamics and cluster impact. The painting shown on the cover is titled surprisal analysis and was dedicated to me by the artist. The topic of surprisal analysis is discussed in Section 6.4.2. The works of Wilf on a variety of scientific themes were exhibited at the Israel National Academy of Sciences and other Institutions. Many paintings by the late Jacob Wilf can be seen at http //j acob. wilf org/... 

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