INDEX surface phenomena

Since oxidation of methanol is an electrocatalytic reaction with different adsorption steps, interactions of the adsorbed species with the metallic surface are important. Using platinum single-crystal electrodes, it has been proven that the electrooxidation of methanol is a surface-sensitive reaction. The initial activity of the Pt(llO) plane is much higher than that of the other low-index planes, but the poisoning phenomenon is so rapid that it causes a fast decrease in the current densities. The... 

The affinity (interaction strength), multiple interactions, and the changes in concentration can be also monitored from those studies. To deliver data in real time, the natural phenomenon of surface plasmon resonance (SPR) is employed. Since the refractive index (r ) at the interface changes as molecules are immobilized on the sensor surface, instant measure of r provides real-time assessment. The Tlcxchip platform exploits grating-coupled SPR (GC-SPR) for this purpose. 

The corrugation inversion due to tip states is a universal phenomenon in the STM imaging of low-Miller-index metal surfaces. For most metals (except several alkali and alkaline earth metals, which have rarely been imaged by STM), the nearest-neighbor atomic distance a 3 A. Consequently, the numerical coefficients on Eq. (5.61) are very close to those for Au(lll). 

Thus the value of the dielectric constant at the sample/metal interface determines the shift of the resonance. When adsorption of molecules at the metal surface results in the change of the refractive index or of the local value of the dielectric constant, the change of reflectivity is observed. This phenomenon has been used as the mechanism for detection of gases (Fig. 9.18a) and of adsorbed biomolecules (Fig. 9.18b). The depth of penetration of the surface plasmon is comparable to that of the evanescent field, that is, 100-500 nm for the visible-near infrared range. 

The phenomenon of soil dispersion with respect to Na+ loads (magnitude of ESP or SAR) appears to be unique to all soils on at least one particular point. As the total salt or Cl- concentration in the water increases, the dispersion index decreases and the saturated hydraulic conductivity increases (Fig. 11.6). When this occurs, the soil-water system becomes toxic to plants and organisms owing to high osmotic pressures. When chloride concentration in solution increases beyond 6000 mg L 1, Na ions near clay surfaces begin to dehydrate because of high osmotic pressure in the surrounding solution. This causes clay particles to flocculate (flocculation is the reverse of dispersion) and, consequently, the saturated hydraulic conductivity of the soil increases. 

To an organic chemist, the more important physical properties of a liquid are the density, refractive index, and boiling point. All three are useful for the characterization of liquids, and the phenomenon of boiling is the basis of the most important method of separating and purifying liquids. Other properties such as the viscosity, surface tension, and dielectric constant are of lesser importance and will not be considered here. 

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