Electron transfer

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Under an electron transfer is the transfer of an electron between two spatially separated centers because of quantum-mechanical transitions. This is a central process of energy transfer on a microscopic scale, which is relevant for chemistry (binding and excitation in molecular systems), based on this for biology as well as for physics and based on this in technologically relevant processes in materials science (e.g. B. semiconductor industry). Depending on the subject, other aspects are related to the term electron transfer .

In chemistry one speaks of electron transfer reaction (also electron transfer reaction) as a reaction to the electron transfer, i.e. rather the macroscopically tangible initial and final state (and thus includes, for example, any approach, e.g. diffusion , of the centers).

In biology , the interplay between electron transfer and the heterogeneous molecular environment is important for the complex processes in biological processes, and is summarized there as the electron transport chain .

Quantum mechanical electron transfer on a microscopic scale also plays a central role in electronic components. However, specific quantum mechanical effects play due to the size of components and the number of electrons and atoms involved. General does not matter and one speaks of electron transport or of macroscopically measurable current. But as soon as an interface is involved, microscopic processes occur that are described by solid-state physics and B. are important in semiconductor technology or photovoltaics .

Classifications (chemistry)

One distinguishes the homogeneous by the heterogeneous electron transfer. The former identifies the exchange within two chemical species (e.g. two molecules ). In heterogeneous electron transfer, the electron is exchanged between an electrode and a chemical species. The electron donor ( donor for short ) releases an electron to the so-called acceptor .

If the donor and acceptor are within one chemical species, one speaks of an intramolecular electron transfer . However, if an electron is exchanged between two species, this form is called intermolecular electron transfer.

If the electron transfer is the chemical mechanism, the redox behavior of the species is a consequence of it. The electron donor is oxidized at the moment of the electron transfer (i.e. its oxidation number increases ), while the acceptor is reduced (i.e. its oxidation number is reduced).

Physical chemistry of electron transfer

Kinetic theories, such as the Marcus theory , try to understand the speed of electron transfer reactions as a consequence of thermodynamic state functions. Quantitative forecasts are only possible in rare cases using the models known today. The description is made more difficult by the enormous number of poorly measurable variables on the one hand and the complexity of the outwardly simple mechanism on the other. More modern models attempt a consistent integration of the diffusion process in theories of the elementary process. The Kramer theories and encounter theories are important here .

Experimental methods for investigating electron transfer are primarily magnetic resonance methods (e.g. electron spin resonance ), relaxation methods (e.g. laser spectroscopy ) and also electrochemical methods (often in combination with the other methods mentioned).

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