Theoretical Studies of Seeded Water Clusters PDF Download

Author: Denise Koch
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Languages : en
Pages : 0

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Book Description
This thesis provides a detailed and thorough theoretical investigation of the solvation structure of ions in water clusters and of solvation effects on photochemically-induced electron transfer processes occurring in seeded aqueous clusters. NaI(H 2 O) n clusters were chosen as a model system for the latter because the electronic structure of NaI is characterized by a curve crossing of ionic and covalent states, and the presence of solvent molecules can significantly affect the NaI electronic structure and photodissociation dynamics due to the differential solvation of these two states. Furthermore, the surface solvation state adopted by large halide ions determines to a great extent the solvation structure of alkali-metal halides in water clusters, and therefore significantly affect their photochemistry. The first-ever rigorous investigation of the solvation thermodynamics of halide-water clusters, presented here, reveals that entropy and polarization drive the ion from a surface to interior solvation structure by cluster size 20 for fluoride, and cluster size 60 for the heavier halides. The outcome of the simulations seems to depend strongly on the choice of model used to describe the system intermolecular interactions, and an array of first-principles simulation methodologies has been designed accordingly. Designing models that allow for solvent polarization and computationally efficient semiempirical methods that can properly describe weak interactions is shown to be essential throughout the thesis. Nonadiabatic simulation techniques were developed, in combination with an hybrid quantum-mechanics/molecular mechanics (QM/MM) model to describe intermolecular interactions, in order to investigate the photodissociation dynamics of NaI(H 2 O) n clusters. Simulation results suggest that the addition of only a few water molecules is sufficient to completely quench the oscillatory NaI dynamics observed in the gas phase, but that the process is dominated by rapid water evaporation. As a result, electron transfer in NaI(H 2 O) n is largely governed by the NaI large-amplitude motion, like in the gas phase, and the solvent only influences the nonadiabatic dynamics by mediating the Nal internuclear separation at which curve crossing occurs. When embedded in an argon matrix, however, the NaI(H 2 O) n nonadiabatic dynamics appears to involve an activationless or activated inverted electron transfer process along the solvent coordinate analogous to what may occur in solution.