Modeling photoexcited reactions of simple molecules in solution.

摘要

Photoexcited iodine in rare gas systems offer a paradigm for understanding excited state condensed phase chemistry. Solvent induced nonadiabaticity plays an important role in the dynamics of these systems and modifies electronic structure by introducing off-diagonal coupling elements to our electronic Hamiltonian matrix. A semi-empirical electronic structure method, diatomics-in-molecules (DIM), together with its extension designed for ionic systems, diatomics-in-ionic-systems (DIIS), is applied to dynamical studies of photoexcited iodine in Ar and Xe rare gas systems. Mixed quantum-classical molecular dynamics implemented using a surface hopping algorithm is employed in a trajectory study which successfully describes the nonadiabatic nature of these systems.;First we looked into the photoexcited I2 in its manifold of covalent states in solid Ar, focusing on the cage-bound but otherwise dissociative potential curves. Cage motions disturb the electronic structure and influence the coupling between electronic states to a large extent due to the large-scale intramolecular motion associated with stretching of the I2 bond resulting from double-photon excitation. Dynamical simulation with a surface hopping algorithm describes the cage-bound state photoexcitation dynamics which has only been simulated by other groups using classical methods that do not allow for nonadiabatic electronic transitions. A characteristic recursion time of the cage-bound state motion is found though our simulation which matches the experimental results, and our simulated pump-probe signals successfully reproduce the experimental spectrum.;Finally we apply our potential model and surface hopping dynamical calculation method to the charge transfer complex Xe+2I- in xenon clusters. The states of this system are accessed at much higher energy than the covalent states. Charge transfer occurs between atoms and requires a significantly more complex potential energy model for which we use an extension to the DITS method that incorporates charge-transfer-to-solvent (CTTS) states. Limited experimental results are available on these systems and they have not been explored in calculations. Our studies thus provide the first microscopic insights into different possible cage exit channels that have been speculated in experimental interpretations.