Nonadiabatic polarization

Nonadiabatic polarization effects have been observed in both Ca and An analysis of the Ba A/ intervals using the adiabatic core... 

A New Approach to the Interaction of the Electron with the Polarization of the Medium in Nonadiabatic Reactions... 

The physical mechanism of entirely nonadiabatic and partially adiabatic transitions is as follows. Due to the fluctuation of the medium polarization, the matching of the zeroth-order energies of the quantum subsystem (electrons and proton) of the initial and final states occurs. In this transitional configuration, q, the subbarrier transition of the proton from the initial potential well to the final one takes place followed by the relaxation of the polarization to the final equilibrium configuration. 

Substrate and intermediate species adsorb on an electrode surface and orient themselves so that their least hindered sides face the electrode, unless there is another effect such as a polar one. An electrode interface has a layered structure in which a nonuniform electric field (some slope of potential) is generated by polarization of the electrode. An extremely strong electric field of approximately 10 V cm i in the innermost layer might cause a variety of polar effects. For instance, electrochemical one-electron oxidation of o-aminophenol derivatives proceeds adiabatically. On the contrary, the homogeneous reaction is nonadiabatic. This difference in behavior is related to... 

In this way the mass polarization term may be removed from the Hamiltonian. However, the resulting electronic wave functions which are obtained are then dependent upon the nuclear masses as well as the nuclear charges and such wave functions are an inconvenient basis from which to investigate nonadiabatic processes. 

Electron transfer (ET) is of course accompanied by rearrangement of the solvent as shown by the horizontal displacement in Figure 26. Tradiational theories for ET fall into two cases. In the nonadiabatic case it is assumed that the rate of ET is controlled by the process of crossing from one electronic state (e.g., LE) to the other (e.g., CT) [60,61]. Alternatively in the weakly adiabatic case, it is assumed that the solvent polarization is always in equilibrium with the changing charge distribution. For this latter case transition state theory is applicable [59]. 

Perhaps the most interesting aspect of microwave spectroscopy of alkaline earth Rydberg states is that it affords easy access to the nonadiabatic effects in core polarization, and such experiments have been done with both Ca6 and Ba.3... 

The 10% difference is probably due to core penetration in the 4snf states, which is not taken into account, and, according to the theoretical work of Vaidyanathan and Shorer12 should be of the same approximate size as the discrepancy. In any case, it is clear that the nonadiabatic core polarization model reproduces the observed intervals quite well, while the adiabatic model is substantially in error. 

While the agreement of the measured and calculated Ba+ quadrupole polarizabilities is not very good, compared to an analysis based on adiabatic core polarization the agreement in Table 17.3 is superb. The adiabatic core polarization model leads to ad = 146flo and aq = —5800. The ground state of Ba+ cannot have a negative quadrupole polarizability. Taken together, the Ca and Ba experiments show clearly that the nonadiabatic effects in core polarization in the alkaline earth atoms are important and may be calculated with some accuracy. 

Nuclear reorganization consists of changes in the internal or vibrational modes of the reactants as well as changes in the nuclear polarization of the surrounding solvent molecules. The distinction between these two classes of nuclear barriers is fundamental in understanding reactivity in photoelectron transfer. With this in mind, we shall now proceed to evaluate the barriers in electron transfer (Fig. 11). The classical theory, to be discussed in the next section, emphasizes the Coulombic and nuclear, whereas in the nonclassical, nonadiabatic theories, which are discussed in Sect. 3.3, emphasis is on electronic and nuclear barriers. 

It is important to realize that the only approximations that enter into this rate expression is the use of the Fenni golden-rule, which is compatible with the weak coupling nonadiabatic limit, and the Condon approximation which is known to be successful in applications to electronic spectroscopy. The solvent effect on the electronic process, including the slow dielectric response, must arise from the FC factor that contains contributions from all the surrounding intermolecular and intramolecular nuclear degrees of freedom. In fact, if the nuclear component of the solvent polarization was the only important nuclear motion in the system, then on the classical level of treatment used by Marcus Eqs (16.53) and (16.51) with Ea given by (16.49) should be equivalent. This implies that in this case... 

Photoinduced electron transfer is a subject characterised, particularly at the present time, by papers with a strongly theoretical content. Solvent relaxation and electron back transfer following photoinduced electron transfer in an ensemble of randomly distributed donors and acceptors, germinate recombination and spatial diffusion a comparison of theoretical models for forward and back electron transfer, rate of translational modes on dynamic solvent effects, forward and reverse transfer in nonadiabatic systems, and a theory of photoinduced twisting dynamics in polar solvents has been applied to the archetypal dimethylaminobenzonitrile in propanol at low temperatures have all been subjects of very detailed study. The last system cited provides an extended model for dual fluorescence in which the effect of the time dependence of the solvent response is taken into account. The mechanism photochemical initiation of reactions involving electron transfer, with particular reference to biological systems, has been discussed by Cusanovich. ... 

Kiefer, P. and Hynes, J. (2004). Kinetic isotope effects for nonadiabatic proton transfer reactions in a polar environment 1 Interpretation of tunneling kinetic isotopic effects. J. Phys. Chem. A. 108, 11793-11808... 

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