Electron transfer, nonadiabatic chemical

Phys. 74 6746 (1981) b) G. L. Gloss, L. T. Calcaterra, N. J. Green, K. W. Penfield, and J. R. Miller, Distance, stereoelectronic effects, and the Marcus inverted region in intramolecular electron transfer in organic radical anions, J. Phys. Chem. 90 3673 (1986). a) S. Larsson, Electron transfer in chemical and biological systems. Orbital rules for nonadiabatic transfer, J. Am. Chem. Soc. 103 4034 (1981) b) S. Larsson, n Systems as bridges for electron transfer between transition metal ions, Chem. Phys. Lett. 90 136 (1982) c) S. Larsson, Electron transfer in proteins, J. Chem. Soc., Faraday Trans. 2 79 1375 (1983) d) S. Larsson, Electron-exchange reaction in aqueous solution, J. Phys. Chem. 88 1321 (1984) e) S. Larsson,... 

The ZN formulas can also be utihzed to formulate a theory for the direct evaluation of thermal rate constant of electronically nonadiabatic chemical reactions based on the idea of transition state theory [27]. This formulation can be further utilized to formulate a theory of electron transfer and an improvement of the celebrated Marcus formula can be done [28]. 

The author would like to thank all the group members in the past and present who carried out all the researches discussed in this chapter Drs. C. Zhu, G. V. Mil nikov, Y. Teranishi, K. Nagaya, A. Kondorskiy, H. Fujisaki, S. Zou, H. Tamura, and P. Oloyede. He is indebted to Professors S. Nanbu and T. Ishida for their contributions, especially on molecular functions and electronic structure calculations. He also thanks Professor Y. Zhao for his work on the nonadiabatic transition state theory and electron transfer. The work was supported by a Grant-in-Aid for Specially Promoted Research on Studies of Nonadiabatic Chemical Dynamics based on the Zhu-Nakamura Theory from MEXT of Japan. 

While studies of specific acid catalysis of redox cofactors shed light on the intricacies of the electron transfer process [54], the conditions required for preprotonation of the cofactor are highly acidic (pH < 0), and would not generally be found in biological systems. There are, however, systems such as Qb reduction in the Rhodobacter sphaeroides reaction center [55], where kinetic data indicate proton transfer prior to or simultaneous with electron transfer. This would seem to indicate that a general acid process is operative. At first glance, this sort of mechanism would seem to be contrary to the Born-Oppenheimer approximation. This apparent paradox can be avoided, however, if quantum chemical (nonadiabatic) processes are considered. 

Nonadiabatic dynamics is a quantum phenomenon which occurs in systems that interact sufficiently strongly with their environments to cause a breakdown of the Born-Oppenheimer approximation. Nonadiabatic transitions play significant roles in many chemical processes such as proton and electron transfer events in solution and biological systems, and in the response of molecules to radiation fields and their subsequent relaxation. Since the bath in which the quantum dynamics of interest occurs often consists of relatively heavy molecules, its evolution can be modeled by classical mechanics to a high degree of accuracy. This observation has led to the development of mixed quantum-classical methods for nonadiabatic processes. 

Using this model they have tried to look at important chemical processes at metal surfaces to deduce the role of electronic nonadiabaticity. In particular, they have tried to evaluate the importance of electron-hole-pair excitation in scattering, sticking and surface mobility of CO on a Cu(100) surface.36,37 Those studies indicated that the magnitude of energy transferred by coupling to the electron bath was significantly less than that coupled to phonons. Thus the role of electron-hole-pair excitation in... 

A second important example where quantum effects need to be taken into account occurs in cases where nuclear motion, for example, in a chemical reaction, leads a molecular system into regions of configurational space where the potential energy surface of the electronic ground state approaches those of one or more excited electronic states. In such cases, it is no longer automatically true that the motion of electrons adapts essentially instantly (or adiabatically) to nuclear motion, and one may have nonadiabatic behavior. Another way of expressing this is that in such regions, nuclear motion can couple to electronic motion, in such a way that the system can be partly transferred into excited electronic states as the atoms move. 

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