Charge distortion

MCP) detectors, respectively. The latter are preferred in TOF instruments since the area of detection is much larger and space charge distortions within the separated ion packets can be minimized. 

A second modification that can be made concerns the use of pseudopotentials on the MM atoms. These provide a more accurate way of accounting for the electrostatic and dispersion interactions between the QM and MM atoms. They enter into the calculation in the same way as the electrostatic interactions — there will be a term for interaction with the nuclei of the QM atoms which is additive and a term which is incorporated into the one-electron matrix. They have been employed to describe the core electrons of atoms in QM calculations and also by Sprik and Klein [76], Estrin et al. [77] and Vaidehi et al. [29] and other groups to describe interactions between QM and MM atoms. Both pseudopotentials and polarizabilities can be included simultaneously as pseudopotentials, in general, do not describe charge distortion effects on the MM atoms. 

Ion-induced dipole forces are one of two types of charge-induced dipole forces, which rely on the polarizability of the components. They result when an ion s charge distorts the electron cloud of a nearby nonpolar molecule. This type of force plays an essential biological role that initiates the binding of the Fe " " ion in hemoglobin and an O2 molecule in the bloodstream. Because an ion increases the magnitude of any nearby dipole, ion-induced dipole forces also contribute to the solubility of salts in less polar solvents, such as LiCl in ethanol. 

An electron flood gun must be used to avoid charging distortions when studying insulators. 

One reason for the importance of proton transfer, acid-base reactions is that the presence of the arriving proton with its positive charge distorts the electron cloud of the base, perhaps exposing an atom nearby in the molecule to attack by other atoms as the electron cloud around it is pulled away. Thus, proton transfer prepares atoms and the bonds that hold them to attack and then further reaction. This preparation for attack is a major role of acid-base reactions in our bodies, with enzymes preparing smaller molecules for digestion or modification. 

The degree to which an electromagnetic wave is slowed down upon entering a given medium depends upon the characteristics of the electronic environment it encounters. This is a function of the individual molecular electron clouds, as well as the number of molecules per unit volume, N (particle density). If the medium contains N molecules per unit volume, the magnitude of the charge distortion in the molecules by the electromagnetic field of the radiation is limited by their polarizibility, a, and the dielectric constant, 8, of the medium. The relationship between these parameters is expressed in the Clausius-Mosotti equation ... 

The single particle band gap of PPV corresponds to a n-n transition [62]. Our calculated value of band gap is 2.0 eV, which is slightly smaller than the experimental value of 2.4 eV [60,63]. Despite this fundamental problem, variations in the band gap produced either by structural or charge distortions, are often more accurately described with density functional methods, and therefore the trends described below should be quite precise... 

Fig. 11. Space charge distortion of the electric field distribution between parallel plate electrodes with spacing d at voltage V so that the average electric field is Eq = V/d. (a) No...

Fig. 6. Kerr pattern in the vicinity of a cathode point, which extends into the drawing from the right of the drawing, is shown in the upper sketch. The lower sketch shows the pattern taken when the injected charge distorts the electric field and, therefore, the Kerr pattern.

Figure 2.30 Selective ejection of an intense peak at a single ra/z reduces the space charge distortion of the mass spectrum. Here, the high m/z selectivity of such resonant excitation is shown for in the presence of Sr+ and Zr+. If is not ejected prior to mass analysis (upper trace), the spectrum is space charge distorted. By ejecting the m/z 89 peak prior to mass analysis, an undistorted spectrum is obtained (lower trace virtually identical to the spectrum of a solution containing only Sr and Zr). Comparison of the spectra shown with spectra of Sr and Zr solutions without Y shows that ejection of Y+ is 50000 times more efficient than ejection of either Sr+ or Zr ...

---