Work term charge transfer

The extent to which steric effects adversely affect the attainment of such intimate ion-pair structures would be reflected in an increase in the work term and concomitant diminution of the inner-sphere rate. This qualitative conclusion accords with the reactivity trend in Figure 16. However, Marcus theory does not provide a quantitative basis for evaluating the variation in the work term of such ion pairs. To obtain the latter we now turn to the Mulliken theory of charge transfer in which the energetics of ion-pair formation evolve directly, and provide quantitative informa-... 

Evaluation of the Work Term from Charge Transfer Spectral Data. The intermolecular interaction leading to the precursor complex in Scheme IV is reminiscent of the electron donor-acceptor or EDA complexes formed between electron donors and acceptors (21). The latter is characterized by the presence of a new absorption band in the electronic spectrum. According to the Mulliken charge transfer (CT) theory for weak EDA complexes, the absorption maximum hv rp corresponds to the vertical (Franck-Condon) transition from the neutral ground state to the polar excited state (22). 

The charge transfer Scheme V is akin to the adiabatic electron transfer cycle in Scheme IV. In this case the work term Wp required to bring the products D+ and A together to the mean separation rp in the CT excited state is given by ... 

Figure 19, Variation of the work term Awp evaluated for various charge-transfer...

Mixed-valence chemistry was reviewed in the late 1960 s both by Robin and Day (4) and by Hush (5). Their work provided the beginnings of a theoretical background for understanding the properties of mixed-valence compounds including the low energy absorption bands which have been termed Intervalence Transfer (IT) or Metal-Metal Charge Transfer (MMCT) bands. 

The visible and near-infrared LID results for NO/Pt were discussed in terms of hot electrons combined with a charge transfer mechanism. For the 193 nm LID result considered here, the photon energy is above the substrate work function, thereby providing a direct source of electrons to bathe the adsorbed NO species. Comparison of translational energy and vibrational state distributions for NO/Pt(lll), NO/Pt(foil), and N0/Ni(100)-0 suggests that the mechanisms driving the desorption processes in these systems might be related. However, the details of the specific interaction potentials must be substantially different to account for the disparate spin-orbit and rotational population distributions. 

The SMO-LMBPT method conveniently uses the transferability of the intracorrelated (one-body) parts of the monomers. This holds, according to our previous results [3-10], at the second (MP2), third (MP3) and fourth (MP4) level of correlation, respectively. The two-body terms (both dispersion and charge-transfer components) have also been already discussed for several systems [3-5]. A transferable property of the two-body interaction energy is valid in the studied He- and Ne-clusters, too [6]. In this work we focus also on the three-body effects which can be calculated in a rather straightforward way using the SMO-LMBPT formalism. 

Finally, we must consider the contribution of the electrostatic work required to transfer one electron into free space. After overcoming the short range chemical forces, the electron must be moved a certain distance against the electric field in the surface. Under the assumption that the lines of force of the electric field are located between the ion defects in the boundary layer and the surface charges represented by the chemisorbed gas atom, we obtain the expression afi for this electrostatic work term. is the boundary field strength represented in Equation (11), and a is the distance between the surface of the oxide and the centers of charge of the chemisorbed atoms in the a-phase. 

The electro-chemical potential fi = /ic + fic, consists of two terms, the electro-static part, fie, and the chemical part, fic, as discussed in the literature13-15. Since the electro-chemical potential is a constant throughout the film thickness, Afi = 0, then A/te =— A/ c. The electro-static part corresponds to the electro-static potential, and reflects the dipole generated by charge transfer at the interface, as seen in the step in the vacuum level in the lower part of Fig. 8.2. The chemical part, in the present case, corresponds to the gradient in the number of particles , which is just the number of electrons transferred (per unit area) from the metal to the polymer at the interface. Since electrons are transferred to the polymer, the gradient in the number of particles works against, and just equals (cancels) the step in the electro-static potential. 

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