Influence of fields

Field Effects. These were discussed on page 16. As an example of the influence of field effects on acidity, we may compare the acidity of acetic acid and nitroacetic acid ... 

Influence of Field Effect. Since electron transfer rates are directly related to the field, a judicious manipulation of the distance of a sensitizer and an electron acceptor (or donor) from a highly charged surface across the Stem layer (Figure 2, equation 7) is expected to result in altered efficiencies. This expectation has been realized In achieving effective charge separation under the Influence of a positive electric field, generated by DODAC vesicles (35). Rate constant for electron transfer from L-cystelne to the excited state of Ru(bpy) ... 

As we have seen, a values may involve some resonance contribution, so the use of cr and cr terms does not totally distinguish between field and resonance effects. Swain and Lupton proposed using discrete field (f) and resonance R) substituent constants (equation 6.94). Instead of a single reaction constant p, two terms measured the influence of field effects (/) and resonance (r) on the reaction. ... 

The argon gas flow proportional counter consists of a cylindrical chamber down the center of which passes a small-diameter wire (the anode), to which a positive potential of between 1 and 2kV is applied (Figure 3). The counter gas, argon, is ionized by incident X-ray photons. Under the influence of fields generated by the applied potential, electrons formed by this ionization process drift toward the wire anode. In the immediate vicinity of the anode, electrons are accelerated by the associated high potential fields, causing further ionization by collision with gas molecules. The resultant avalanche of electrons caused... 

As electron diffraction provides direct measurement of interatomie distanees, it is an ideal method for the determination of the molecular stmcmres of gases. Moreover, moleeules in the gas phase are free from the intermolecular interactions and the influence of fields that ean distort a structure (particularly the conformation) in the crystalline state, or even change it completely. We will see some examples of this in the case histories presented in Chapter 12. But there are, of course, limits to the usefiilness of electron diffraction, of which the most obvious is that gaseous samples are needed. The essential requirement is that the compound to be smdied should have a vapor pressure of about 1 mbar at a temperature at which it is stable. Lower vapor pressures can be used, but the experiments are more difficult to perform. As long as no decomposition occurs, the temperature does not really matter, and such involatile species as alkali metal halides or lanthanide halides and some metal oxides have been studied at temperatures of up to 2000 K or more. However, we should remember that raising the sample temperamre increases amplitudes of vibration, and can change the relative populations of isomers or conformers. 

Seljasen, R., et al. (2013). Influence of field attack by carrot psyllid (Trioza apicaUs Forster) on sensory quality, antioxidant capacity content of Terpenes, Falcarindol 6-MethoxymeUein of carrots (Daucuscarota L.). Journal of Agricultural Food Chemistry, 6i(ll), 2831-2838. 

Figure 47. Storage effect in liquid crystals with negative dielectric anisotropy. Schematic of the texture changes under the influence of field strength and frequency (after reference [110]).

It is not superfluous to point out that the relationship between wave-mechanical frequency and mechanical energy assumed here is hypothetical throughout, since we know that already the Lorentz force law, which regulates the influence of fields on matter, is replaced by something completely different, namely the wave equation. 

Chapter 5, which discusses the influence of fields on flames, is primarily an application of the equations established for homogeneous media. 

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