Charge field effect

As far as photoelectrochemical processes are concerned, the most important physical process is the space-charge field effect on the carrier distribution. As discnssed, the... 

Tsong, T. Y. Astumian, R. D. Charge-field interactions in cell membranes and electroconformational coupling Transduction of electric energy by membrane ATPase. In Charge-Field Effects in Biosystems Allen, M. J., Ed. Plenum New York Vol. II, pp 167-177. 

A. C. de Dios and E. Oldfield, Chem, Phys, Lett., 20S, 108 (1993). Methods for Computing Nuclear Magnetic Resonance Chemical Shielding in Large Systems. Multiple Cluster and Charge Field Effects. 

Figure Bl.22.4. Differential IR absorption spectra from a metal-oxide silicon field-effect transistor (MOSFET) as a fiinction of gate voltage (or inversion layer density, n, which is the parameter reported in the figure). Clear peaks are seen in these spectra for the 0-1, 0-2 and 0-3 inter-electric-field subband transitions that develop for charge carriers when confined to a narrow (<100 A) region near the oxide-semiconductor interface. The inset shows a schematic representation of the attenuated total reflection (ATR) arrangement used in these experiments. These data provide an example of the use of ATR IR spectroscopy for the probing of electronic states in semiconductor surfaces [44]-...

Chemical and biological sensors (qv) are important appHcations of LB films. In field-effect devices, the tunneling current is a function of the dielectric constant of the organic film (85—90). For example, NO2, an electron acceptor, has been detected by a phthalocyanine (or a porphyrin) LB film. The mechanism of the reaction is a partial oxidation that introduces charge carriers into the film, thus changing its band gap and as a result, its dc-conductivity. Field-effect devices are very sensitive, but not selective. 

Electronegative, nonconjugating groups (which interact with an incipient carbocation only by an inductive or field effect) discourage attack at C. This is due to destabilization of transition state (49) by the juxtaposition of positive charge. 

Field effects can be determined by calculating the effect of a bond dipole on a molecular probe at a specifted distance. One system that has been examined is H2 aligned with an H—X molecule. The substituent effect is related to the charge which develops at Ha, relative to the case where X = H. 

The leaving group also affects the amount of internal versus terminal alkene that is formed. The poorer the leaving group, the more El cb-like is the transition state. This trend is illustrated for the case of the 2-butyl system by the data in Table 6.6. Positively charged leaving groups, such as in dimethylsulfonium and trimethylammonium salts, may favor a more El cb-like transition state because their inductive and field effects increase the acidity of the p protons. 

In view of the magnitude of crystal-field effects it is not surprising that the spectra of actinide ions are sensitive to the latter s environment and, in contrast to the lanthanides, may change drastically from one compound to another. Unfortunately, because of the complexity of the spectra and the low symmetry of many of the complexes, spectra are not easily used as a means of deducing stereochemistry except when used as fingerprints for comparison with spectra of previously characterized compounds. However, the dependence on ligand concentration of the positions and intensities, especially of the charge-transfer bands, can profitably be used to estimate stability constants. 

CT-bond or field effect, is considered herein to arise primarily from inductive stabilization of the resonating negative charge in the transition state. 

The field, of strength E, is assumed in the z-direction the charge of the electron is e no magnetic field effects are considered, since the electron velocities are assumed small compared with the velocity of light.26 The Boltzmann equation is thus... 

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