Inter-site excitation

The local or extended nature of molecular-ion (or exciton) states in molecular solids is determined by a competition between fluctuations in the local site energies of these states (which tend to localize them) and the hopping integrals for inter-site excitation transfer (which tend to delocalize them). In order to define this fluctuation-induced localization concept more precisely, consider the model defined by the one-electron Hamiltonian... 

The effect of inter-site hopping is then introduced into the system. The manifold of basis states are limited to those in which the local correlations have been diagonalized. The wave functions for the composite particles then obey Bloch s theorem, which results in the formation of a dispersion relation consisting of two bands for the quasi-bosons the first band describes spinless quasi-boson excitations, the second band describes the magnetic quasi-bosons. Although these composite particles are bosons in that they commute on different sites, they nevertheless have local occupation numbers which are Fermi-Dirac like. 

It means that for electrons which satisfy condition of extreme nonadiabaticity (antiadiabaticity with respect to interacting phonon mode r in particular direction of reciprocal lattice where the gap in one-electron spectrum has been opened), the electron (nonadiabatic polaron)-renormalized phonon interaction energy equals zero. Expressed explicitly, in the presence of external electric potential, dissipation-less motion of relevant valence band electrons (holes) on the lattice scale can be induced at the Fermi level (electric resistance p = 0). At the same time, the motion of nuclei remains bound to circumferential revolution over distorted, energetically equivalent, configurations. The electrons move in a form of itinerant-mobile bipolarons, i.e. as a polarized cloud of inter-site charge density distribution- sequence b, d, e, f, b, d, e, f. in Fig. 27.6. For temperature increase, thermal excitations of valence band electrons to conduction band induce sudden transition from the antiadiabatic state to adiabatic state at T — 7, i.e. < AEd Rd) holds and the system is... 

In brief, irradiation leads to the sub-picosecond oxidation of the Re(I) center and the production of a mixture of two reduction sites i.e. either the MQ+ or dmb ligand can be reduced. On the time-scale of several picoseconds inter-ligand electron transfer occurs, converting the mixture of excited states to [Ren(MQ )(CO)3(dmb)]2+. 

In (1), Hq yields the total energy of system in which the molecules and the lattice are excited, yet there are no interactions between molecules and the lattice. The transfer of an electron from site m to site n is given by //j. Polaronic effects, i.e., effects due to the interaction of the electronic excitation and the lattice, are given by H2 and H. hi H2, the energy of the site is reduced by the interaction with the lattice vibration. In H, the lattice vibration alters the transition probability amplitude from site m to n. The term lattice vibration may refer to inter-molecular or intra-molecular vibrations. Static disorder effects are considered in H4, which describes the changes to the site energy or transition probabihty amplitude by variations in the structure of the molecular sohd. 

Bidirectional PCET is also featured on the reduction side of the photosynthetic apparatus. In the bacterial photosynthetic reaction center, two sequential photo-induced ET reactions from the P680 excited state to a quinone molecule (Qg) are coupled to the uptake of two protons to form the hydroquinone [213-215]. This diffuses into the inter-membrane quinone pool and is re-oxidized at the Qq binding site of the cytochrome bcj and coupled to translocation of the protons across the membrane, thereby driving ATP production. These PCET reactions are best described by a Type D mechanism because the PCET of Qg appears to involve specifically engineered PT coordinates among amino acid residues [215]. In this case PT ultimately takes place to and from the bulk solvent. Coupling remains tight in... 

The proximity of the excited J = l multiplet to the ground / = f multiplet (AE 1500 K) has a profound effect on the susceptibility as demonstrated by its increase with the temperature (fig. 6.25). Because the crystal field induces admixtures of the different multiplets, the susceptibility does not follow the simple Van Vleck (1932) theory. Although de Wijn et al. (1973) managed to extract information on the crystal field parameters in some Sm cubic inter-metallic compounds, the presence of two types of crystallographic site in Sm metal prohibits, at present, a detailed comparison in this case. 

For efficient luminescence of Ln, the inter-ionic nonradiative rate is decreased by diluting the ion into a transparent host lattice. Thus, fast migration between ions, for which the excitation finally ends up at defect or killer sites, and energy transfer between ions [24] are both minimized. 

Excited-state Phenomena.—Czarniecki and Breslow provide an experimental test for structure and organization in micelles and vesicles based on inter-molecular hydrogen-atom abstraction by benzophenone triplet-state. This leads to functionalization at a particular site in the chain, which may be identified by degradation and mass spectrometry. With didodecyl phosphate and (97) or (98), the specificity is as shown (Figure 9) for sonicated surfactant, presumed to be in vesicular form. This shows a much altered specificity from the corresponding reaction in micelles. When sonication is carried out in a sodium borate buffer, a technique considered to provide multilamellar layers (opaque dispersion ) then the terminal selectivity is completely lost and C(6) is the most favoured site for attack. 

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