Thermodynamics of electron trapping

Thermodynamics of Electron Trapping and Electron Solvation in Liquid Hydrocarbons... 

THERMODYNAMICS OF ELECTRON TRAPPING AND ELECTRON SOLVATION IN LIQUID HYDROCARBONS... 

Thermodynamics of Electron Trapping and Solvation in the Quasi-ballistic Model... 

Mozumder (1996) has discussed the thermodynamics of electron trapping and solvation, as well as that of reversible attachment-detachment reactions, within the context of the quasi-ballistic model of electron transport. In this model, as in the usual trapping model, the electron reacts with the solute mostly in the quasi-free state, in which it has an overwhelmingly high rate of reaction, even though it resides mostly in the trapped state (Allen and Holroyd, 1974 Allen et ah, 1975 Mozumder, 1995b). Overall equilibrium for the reversible reaction with a solute A is then represented as... 

Baird and Rehfeld (1987) have analyzed the thermodynamics of electron transport in the two-state trapping model. According to these authors, the effective mobility, ignoring the mobility in the trapped state, is given by... 

For instance, the more efficiently the photoholes are trapped from the valence band of an n-type semiconductor, the higher is the probability that the photoelectrons in the conduction band reach the surface and can reduce a thermodynamically suitable electron acceptor at the solid-liquid interface. This is illustrated with an example taken from a paper by Frei et al, 1990. In this example methylviologen, MV2+, acts as the electron acceptor and TiC>2 as the photocatalyst. Upon absorption of light with energy equal or higher than the band-gap energy of Ti02, a photoelectron is formed in the conduction band and a photohole in the valence band ... 

There has been a resurgence of interest in proton-coupled redox reactions because of their importance in catalysis, molecular electronics and biological systems. For example, thin films of materials that undergo coupled electron and proton transfer reactions are attractive model systems for developing catalysts that function by hydrogen atom and hydride transfer mechanisms [4]. In the field of molecular electronics, protonation provides the possibility that electrons may be trapped in a particular redox site, thus giving rise to molecular switches [5]. In biological systems, the kinetics and thermodynamics of redox reactions are often controlled by enzyme-mediated acid-base reactions. 

These results indicate that the transition from surface state III to surface state II is thermodynamically favorable. The redox potential of the trapped site coordinated with one carboxyl groups is less negative than the redox potential of the site coordinated with two carboxyl groups simultaneously. On this basis the energy level diagram of the electron trapped sites was proposed (Fig. 6). Such temperature transformations are typical for Pb doped and pure aqueous colloidal solutions. When the temperature is raised to room temperature for Pb ion doped solution, all photogenerated electrons are scavenged by metal ions,... 

The nature of the lowest-lying excited states of the fullerenes has been difficult to identify with much certainty. From Shpol skii-type luminescence spectra recorded at 1.5 K it has been concluded that the first-excited singlet state in C70 is of A 2 character. The origins of the lowest energy transitions in Ceo, namely Si(T]g) and S2(Gg), have been assigned on the basis of fluorescence and excitation spectra, supported by theoretical calculations. " The luminescence properties and relaxation dynamics of single crystals of Qo have been described while related measurements have been made for solid films of Ceo " Similar studies have reported the luminescence spectral properties of 50 trapped inside the cavities of NiY zeolites. An analysis of the fine structure of electron-vibrational spectra has been made for 50 and its derivatives in a solid toluene matrix. The rate of triplet energy transfer between fullerenes in toluene solution has been measured as a function of temperature and used to derive thermodynamic parameters for the transfer process. ... 

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