Heterogeneous electron transfer (HET): the redistribution of charge from a single donating electronic state to an accepting continuum, is a crucial step for many phenomena both of fundamental interest and with regard to application. For instance, desorption induced by electronic transitions or the field of photochemistry, and charge carrier separation in, for example, quantum dot-based solar cells. Depending on the electronic interaction of donor (D) and acceptor (A), two limiting cases, the strong and the weak coupling limit arc defined and treated differently by theory. ln the former, the electronic coupling is assumed to be sufficiently strong to describe the transfer reaction in the adiabatic limit where wave packet propagation occurs along a steady potential; this treatment is particularly appropriate when the characteristic charge transfer time is small compared to the nuclear motion of the donor (Franck-Condon approximation). This limit of HET will be discussed in Section 4.1. Approaching the nonadiabatic case for weak clectronic interaction between donor and acceptor, Section 4.1.4 discusses the elastic electron transfer from a small adsorbate that impinges on the substrate on timcscales on the order of the transfer event. Section 4.2 discusses the treatment of HET on the basis of Marcus theory where complex nuclear motions in polar or polarizable media strongly influence the charge transfer rate.
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978-3-527-40924-2