Understanding the Photodissociation Dynamics of Molecular Cluster Ions

<p>The effects of solvation on the photodissociation and recombination of I-2<br /> are studied through nonadiabatic molecular dynamics simulations, using an effective Hamiltonian<br /> that accounts for the strong perturbation of the solute electronic structure by<br /> the solvent. Methods for analyzing the simulations are developed, including a two dimensional<br /> model for the excited stated dynamics, derived from the theory of electron<br /> transfer reactions in solution.</p> <p>The primary focus is understanding the photodissociation of I-2 (CO2)n clusters.<br /> The experimental absorption recovery signal for clusters with n \&gt; 13 features an enhanced<br /> absorption peak, 2 ps after the initial excitation of I-2. We present evidence<br /> that this feature is due to transitions from the ground state to the spin-orbit excited<br /> states, rather than to excited-state absorption as previously assigned. Previously, this<br /> possibility was ruled out because the experiments also indicated that the final products<br /> contained I-2 in its lower spin orbit state and there was no known mechanism for spin orbit<br /> relaxation occuring on the experimental detection timescale. Simulations of the<br /> photodissociation of I-2 (CO2)n clusters at 395 nm reveal an efficient mechanism for the<br /> spin-orbit relaxation of I-2 via a solvent mediated charge transfer process, and this has<br /> subsequently been observed experimentally.</p> <p>The existence of a strong absorption from the ground state of I-2 to the spin-orbit<br /> excited states affects the interpretation of other experimental measurements on these<br /> systems. The dynamics simulations of I-2(CO2)n and I-2 Arn clusters are analyzed in an<br /> effort to shed light on the experimental results.</p>
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University of Colorado Boulder
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