| Abstract
| - Two different mechanistic processes in intramolecular electron transfer chemistry have been studiedwith the complete active space self-consistent field quantum chemical method for a model bis(hydrazine)radical cation. These correspond to (a) a chemical electron transfer, where a reaction intermediate or a transitionstructure exist with the charge localized on the linker, and (b) a nonadiabatic electron transfer, where thebridge remains neutral. These processes coexist on the same potential energy surface. They are characterizedby very different reaction coordinates and are thus distinct elements of the mechanistic spectrum of intramolecularelectron transfer in organic radical cations. The energetically favored chemical electron-transfer process involvesconventional reaction paths. In contrast, the nonadiabatic electron-transfer process involves an unconventionalreaction path, which connects reactant and products via an un-avoided (i.e., real) crossing seam (i.e. an (n −1)-dimensional intersection, where n is the number of vibrational degrees of freedom of the system) betweentwo different adiabatic potential energy surfaces. Our results, computed for a model compound, differ fromNelsen's experimental results, and thus demonstrate the importance of the hydrazine substituents and the aromaticspacer.
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