Back electron transfer description

A more quantitative description of the photocurrent responses, taking into account the contributions from back electron transfer and RuQi attenuation, was achieved by IMPS measurements [83]. Considering the mechanism in Fig. 11, excluding the supersensitization step, and the equivalent circuit in Fig. 18, the frequency-dependent photocurrent for a perturbation as in Eq. (42) is given by... 

The kinetic results from the time-resolved experiments show that back electron transfer leading to annihilation of Mn(CO), actually proceeds by second-order kinetics, with the rate constant being 3 X 1010 A/-1 second-1. As such, any description of the photostationary state attained in the absence of additives must include the diffusive separation of the initial... 

Scheme 1. Schematic description of primary processes occurring during a semiconductor photocatalyzed redox reaction. The thick vertical bar symbolizes the solid/liquid interface. For the sake of simplicity emissive and photocorrosive processes are omitted. (1) Light absorption and primary charge recombination (2) charge trapping at unreactive or (3) reactive surface sites (4, 5) secondary charge recombination (6, 7) IFET processes (8) back electron transfer (9, 10) secondary reactions.

Figure 1. Schematic description of the photoredox reaction A + D = Arcd + Dox catalyzed by a platinized semieonduetor, a typieal example of semieonduetor photocatalysis type A for secondary back electron transfer, see Eqs. 7 and 8.

In any mixed-valence compound, the first problem to be addressed is one of description. Is the compound localized or "delocalized In a localized description the stationary state quantum mechanical solution for the odd electron is oscillatory in nature and has the electron transferring back and forth between the metal ion sites. Spectroscopic data are available for... 

Let us begin with the one-mode electron-transfer system. Model IVa, which still exhibits relatively simple oscillatory population dynamics [205]. SimUar to what is found in Fig. 5 for the mean-field description, the SH results shown in Fig. 13 are seen to qualitatively reproduce both diabatic and adiabatic populations, at least for short times. A closer inspection shows that the SH results underestimate the back transfer of the adiabatic population at t 50 and 80 fs. This is because the back reaction would require energetically forbidden electronic transitions which are not possible in the SH algorithm. Figure 13 also shows the SH results for the electronic coherence which are found to... 

How does the electron transfer occur in a redox process One description of this process was developed by Gerischer, based on the former work of Gurney and Essin. Another description goes back to the work of Marcus.Other contributions during the development of the basic theory came from Dogonadze, Levich, Chizmadzhev, Kuznetsov, and others. The model will be described for a simple redox reaction, the oxidation of a two-valent iron ion into a three-valent iron ion and vice versa. 

These descriptions snggest that iron, when forming chemical compounds, takes the form of Fe(II) or Fe(III). And it can go back and forth between Fe(II) andFe(III) readily. Fe(II) gives off an electron to become Fe(III), and Fe(III) becomes Fe(II) when it accepts an electron. This kind of process is also called electron transfer reaction. Hence, iron (in the form of Fe(II) and Fe(III)) can readily undergo an electron transfer reaction or alternatively an oxidation-reduction reaction, because the process of Fe(II)s becoming Fe(III) is an oxidation and the reverse (Fe(III) —>Fe(II)) is a reduction reaction. 

A simple description of the charge transfer process in molecular orbital terms is that electron density is back-donated from metal d-bands into the CO ir orbital, which is anti-bonding in character (14). The relatively small size of the frequency shift implies that the extent of charge transfer is small. As a result, the C-0 bond order is still close to 3.0 for linearly adsorbed molecules. 

Very stable alkene complexes of this type are formed by metal atoms that can contribute not only the vacant AO into which to draw electronic charge from the fitted carbon-carbon n-bonding MO [Fig. 1.14(a), (i)], but also a filled pd hybrid AO that can transfer electronic charge back into the alkene s empty K-antibonding MO [Fig. 1.14(a), (ii)]. The net result is to convert the MCC triatomic system from a four-electron, five-AO system in the case of a metal like aluminum [Fig. 14(b), (i)] into a six-electron, six-AO system for a metal like platinum, for which an electron-precise bonding description is possible [Fig. 1.14(b), (ii)]. 

N = 1.0976 for free N2), consistent with back-donation of electron density from Ru" to N2." A molecular orbital description for (58) has been discussed. (58) shows a metal ligand charge transfer band at 263 nm ( = 4.8 x 10 M cm Replacement ofNHj by HjO in the dimer decreases hH of binding of N2 by 25.1 kJmol . " The "N NMR of (58) has been reported recently."" ... 

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