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Understanding the Photodissociation Dynamics of Molecular Cluster Ions

TitleUnderstanding the Photodissociation Dynamics of Molecular Cluster Ions
Publication TypeThesis
Year of Publication1999
AuthorsDelaney, ND

The effects of solvation on the photodissociation and recombination of I-2
are studied through nonadiabatic molecular dynamics simulations, using an effective Hamiltonian
that accounts for the strong perturbation of the solute electronic structure by
the solvent. Methods for analyzing the simulations are developed, including a two dimensional
model for the excited stated dynamics, derived from the theory of electron
transfer reactions in solution.

The primary focus is understanding the photodissociation of I-2 (CO2)n clusters.
The experimental absorption recovery signal for clusters with n > 13 features an enhanced
absorption peak, 2 ps after the initial excitation of I-2. We present evidence
that this feature is due to transitions from the ground state to the spin-orbit excited
states, rather than to excited-state absorption as previously assigned. Previously, this
possibility was ruled out because the experiments also indicated that the final products
contained I-2 in its lower spin orbit state and there was no known mechanism for spin orbit
relaxation occuring on the experimental detection timescale. Simulations of the
photodissociation of I-2 (CO2)n clusters at 395 nm reveal an efficient mechanism for the
spin-orbit relaxation of I-2 via a solvent mediated charge transfer process, and this has
subsequently been observed experimentally.

The existence of a strong absorption from the ground state of I-2 to the spin-orbit
excited states affects the interpretation of other experimental measurements on these
systems. The dynamics simulations of I-2(CO2)n and I-2 Arn clusters are analyzed in an
effort to shed light on the experimental results.