Laser induced charge transfer reactions of halogens in rare gas solids and liquids provide a powerful means for the study of condensed phase dynamics. Many-body effects with respect to both electronic and nuclear coordinates, and cooperative interactions with radiation fields, are some of the studied phenomena that are highlighted in this article.The pertinence of these ionic reactions to chemistry in solids is demonstrated in photodissociation studies of molecular halogens in rare gas matrices. The coexistence of both delocalized and localized charge transfer states in solid xenon doped with atomic halogens is presented and dynamical consequences—charge separation, self-trapping and energy storage—are discussed. Static and dynamic solvent effects in liquid phase harpoon reactions are considered. The characterization of cooperative excitations— two-photon, two-electron transitions—in liquid solutions is presented.

Two-photon-induced harpoon reactions of IC1 in liquid and solid xenon are reported. The reaction dynamics is followed by monitoring the luminescent products: the triatomic Xe2Cl and Xe21 exciplexes. Action spectra and branching ratios as a function of excitation energy are reported. The efficient production of the nonthermodynamic product, the iodide, in the liquid phase implies that the cage exit of the ejected C1 atom is direct and sudden. The absence of iodide in the crystalline solids establishes the absence of direct cage exit in the ordered phase. Line-shift.measurements at the phase transition indicate that the exciplexes are strongly clustered in the liquid phase. The effect of clustering on dynamics is the prevention of exchange between iodide and chlorine-the solvent cage excludes C1 atoms. Branching ratios and action spectra are used to identify the potential surfaces in the exit channel and the optical resonances in the entrance channel. The two-photon charge-transfer excitations are enhanced by two-electron resonances that allow selectivity of products.

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lation suggesting that the stable conformation of the radical is planar,9 and thus it might be possible to assert that the circumstances of the canal complex make the nonplanar structure stable. If the above assertion is true, it follows that the most stable conformation (S) is pyramidal and the next stable one (U) is planar as in the MINDO calculation. These two structures cannot exist at the same time unless unreasonable structures are assumed.However, if a pyramidal conformation is the most stable at the equilibrium state, it is reasonable to suppose that the next stable (9) Igual, J. THEOCHEM 1985, 121, 221. one is its inverse conformation. This is the present case.In conclusion, the structure of the methylcyclohexyl radical is pyramidal at the equilibrium state and the angle of CCC is about 117°. At the low temperature, there are two nonplanar conformations and the radical does the umbrella inversion between these conformations. The existence of the wall of thiourea makes it possible to observe this inversion. At the higher temperatures, this umbrella inversion occurs rapidly and the radical can be thought to be planar.