Donor acceptor potential energy surface

In many instances tire adiabatic ET rate expression overestimates tire rate by a considerable amount. In some circumstances simply fonning tire tire activated state geometry in tire encounter complex does not lead to ET. This situation arises when tire donor and acceptor groups are very weakly coupled electronically, and tire reaction is said to be nonadiabatic. As tire geometry of tire system fluctuates, tire species do not move on tire lowest potential energy surface from reactants to products. That is, fluctuations into activated complex geometries can occur millions of times prior to a productive electron transfer event. 

Effect of diagonal-off-diagonal dynamic disorder (D-off-DDD). The polarization fluctuations and the local vibrations give rise to variation of the electron densities in the donor and the acceptor, i.e., they lead to a modulation of the electron wave functions A and B. This leads to a modulation of the overlapping of the electron clouds of the donor and the acceptor and hence to a different transmission coefficient from that calculated in the approximation of constant electron density (ACED). This modulation may change the path of transition on the potential energy surfaces. 

The dicarboxonium ions would be useful intermediates for the diacylation of aromatics. The 1,2-dicarboxonium ion (oxalyl dication, 17) has yet to be experimentally obtained. The ionization of the oxalyl fluoride in SbFs presumably forms the donor-acceptor complex, 18, which spontaneously decomposes to CO and COF2. The expected oxalyl dication (OCCO), 17, was not observed although theoretical calculations at MP2/6-31G level indicate 17 to be a minimum on the potential energy surface. 

Fig. 1. The potential energy surface for the nuclear motion in the cases of electron localization on the core of the donor, Jl/ (q), and on the core of the acceptor, 7/r(<7). q is the nuclear coordinate, -tt,(q ) is the activation energy of the electron transfer in the case of the classical nuclear motion, J is the reaction exothermicity, and Er is the reorganization energy.

Fig. 2. The potential energy surface for the electron motion from a donor to an acceptor in a condensed medium. U,t(r) and Ut, (r) are the potentials of the cores of the donor and the acceptor, the rest of the potentials are created by the molecules of the medium r is the electron coordinate, and R is the distance between the donor and the acceptor. The broken horizontal line corresponds to the under barrier electron motion from the donor to the acceptor. I is the height of the barrier for tunneling.

The rate of a given reaction depends on the thermal activation conditions of the particle in donor and acceptor, factors which are accounted for in the Marcus model [6,7] or models where the vibrational wave functions are included [8-10], The reaction rate is derived in rather much the same way as for ordinary chemical reactions, using the concept of potential energy surfaces (PES s) [6]. The electronic factor is introduced either as a matrix element H]2 or as an... 

In the Marcus model the important part of the system is donor and acceptor and the process takes place on the potential energy surface of the ground state of the total system, while the first excited state corresponds to the remaining, upper parts of the Marcus parabolas. If eq.(4) is solved, a number of excited states correspond to excitations of the bridge. It is interesting to... 

Although the fully formed dicationic structure (12) is not formed, the donor-acceptor complex 11 may have partial superelectrophilic character by interaction with SbFs. The adamanta-l,3-diyl dication 12 has been found to be the global minimum structure on the CioHi42+ potential energy surface.5 Theoretical studies at the B3LYP/6-31G level have shown 12 to be 0.4kcal/mol more stable than the isomeric 1,4-dication... 

Figure 2.1(a) above illustrates the potential energy surface for a diabatic electron transfer process. In a diabatic (or non-adiabatic) reaction, the electronic coupling between donor and acceptor is weak and, consequently, the probability of crossover between the product and reactant surfaces will be small, i.e. for diabatic electron transfer /cei, the electronic transmission factor, is transition state appears as a sharp cusp and the system must cross over the transition state onto a new potential energy surface in order for electron transfer to occur. Longdistance electron transfers tend to be diabatic because of the reduced coupling between donor and acceptor components this is discussed in more detail below in Section 2.2.2. 

Figure 3-5. Potential energy surface for the water dimer obtained at RHF/DZP and QM/MM levels. Solid line RHF dotted donor QM dashed acceptor QM...

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