Electron-transfer reaction optical process

Controlled-potential (potentiostatic) techniques deal with the study of charge-transfer processes at the electrode-solution interface, and are based on dynamic (no zero current) situations. Here, the electrode potential is being used to derive an electron-transfer reaction and the resultant current is measured. The role of the potential is analogous to that of the wavelength in optical measurements. Such a controllable parameter can be viewed as electron pressure, which forces the chemical species to gain or lose an electron (reduction or oxidation, respectively). 

Does T differ significantly from unity in typical electron transfer reactions It is difficult to get direct evidence for nuclear tunnelling from rate measurements except at very low temperatures in certain systems. Nuclear tunnelling is a consequence of the quantum nature of oscillators involved in the process. For the corresponding optical transfer, it is easy to see this property when one measures the temperature dependence of the intervalence band profile in a dynamically-trapped mixed-valence system. The second moment of the band,... 

Chrom means colour and electro implies an electrochemical process, so electrochromic means colour change or generation of a new optical absorption band caused by an electron-transfer reaction. 

Electron transfer reactions and spectroscopic charge-transfer transitions have been extensively studied, and it has been shown that both processes can be described with a similar theoretical formalism. The activation energy of the thermal process and the transition energy of the optical process are each determined by two factors one due to the difference in electron affinity of the donor and acceptor sites, and the other arising from the fact that the electronically excited state is a nonequilibrium state with respect to atomic motion (P ranck Condon principle). Theories of electron transfer have been concerned with predicting the magnitude of the Franck-Condon barrier but, in the field of thermal electron transfer kinetics, direct comparisons between theory and experimental data have been possible only to a limited extent. One difficulty is that in kinetic studies it is generally difficult to separate the electron transfer process from the complex formation... 

Earlier studies on dye-sensitized Ti02 reported nanosecond time constants for the injection kinetics [16, 40-42]. These results were obtained indirectly from the measurement of the injection quantum yield and implicitly assumed that the interfacial electron transfer reaction was competing only with the decay of the dye excited state. Other studies were based on the same assumption but used measurements of the dye fluorescence lifetime, which provided picosecond-femtosecond time resolution [43-45]. Direct time-resolved observation of the buildup of the optical absorption due to the oxidized dye species S+ has been employed in more recent studies [46-51]. This appears to be a more reliable way of monitoring the charge injection process as it does not require any initial assumption on the sensitizing mechanism. 

Electron transfer plays an important role in many physical, chemical and biological processes [1,2,16]. Biological processes such as photosynthesis and respiration involve a series of reactions which are effectively controlled by electron transfer. Electron transfer reactions occur on a timescale of femtoseconds to seconds and over distances of less than 0.1 nm to about Inm. Technologically important processes like redox catalysis, solar energy conversion, non-linear optics and information storage devices provide a few examples of areas where electron transfer is important. 

In the previous sections, we have discussed electron transfer reactions between optically excited molecules and semiconductor electrodes. The question arises whether the opposite effect, the production of an excited state by electron transfer, is also possible. In principle it can be realized if we select a semiconductor, the conduction band (c.b.) of which is located above the energy level of the excited species [ f(M /M )]. The reaction process is then given by... 

Electron Transfer Reactions Coherent Control OF Chemical Reactions Lasers, Ultrafast Pulse ItecHNOLOGY Luminescence Molecular Beam Epitaxy, Semiconductors Nanostructured Materials, Chemistry of Noni.inf.ar Optical Processes... 

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