Nature of Adsorbate

OSEE Optically stimulated exoelectron emission [143] Light falling on a surface in a potential held produces electron emission Presence and nature of adsorbates... 

LA Light absorption [192, 193] UV-visible adsorption by Nature of adsorbed species... 

All gases below their critical temperature tend to adsorb as a result of general van der Waals interactions with the solid surface. In this case of physical adsorption, as it is called, interest centers on the size and nature of adsorbent-adsorbate interactions and on those between adsorbate molecules. There is concern about the degree of heterogeneity of the surface and with the extent to which adsorbed molecules possess translational and internal degrees of freedom. 

Though as yet in its infancy, the application of laser Raman spectroscopy to the study of the nature of adsorbed species appears certain to provide unusually detailed information on the structure of oxide surfaces, the adsorptive properties of natural and synthetic zeolites, the nature of adsorbate-adsorbent interaction, and the mechanism of surface reactions. 

The EMIRS and SNIFTIRS methods provide the IR vibrational spectra (really the difference spectra - see later) of all species whose population changes either on the electrode surface or in the electrical double layer or in the diffusion layer in response to changing the electrode potential. Spectra will also be obtained for adsorbed species whose population does not change but which undergo a change in orientation or for which the electrode potential alters the Intensity, the position or shape of IR absorption bands. Shifts in band maxima with potential at constant coverage (d nax 6 very common for adsorbed species and they provide valuable information on the nature of adsorbate/absorbent bonding and hence also additional data on adsorbate orientation. 

In addition to the structure and composition of the electrode, evaluation of an electrochemical interface in terms of the nature of adsorbates has long been recognized as a... 

A detailed description is given to the role of point defects available in the volume and on the surface of oxide adsorbents on adsorption-induced change of electrophysical characteristics. We try to deduce the impact of the proper nature of adsorbent as well as the nature of adsorption centers. 

The effect of the nature of adsorbent on adsorption-caused change in its electrophysical characteristics. The nature of adsorption centers and their effect on the process of charging of the surface... 

All major characteristics of chemisorption response of electrophysical parameters of semiconductor adsorbents such as sensitivity, selectivity, inertia, reversibility are naturally dependent both on the nature of adsorbent and on chemical activity of absorbate with respect to adsorbent chosen. 

It has been proven by experiment that there are donor acceptor atoms and molecules of absorbate and their classification as belonging to one or another type is controlled not only by their chemical nature but by the nature of adsorbent as well (see, for instance [18, 21, 203-205]). From the standpoint of the electron theory of chemisorption it became possible to explain the effect of electron adsorption [206] as well as phenomenon of luminescence of radical recombination during chemisorption [207]. The experimental proof was given to the capability of changing of one form of chemisorption into another during change in the value of the Fermi level in adsorbent [208]. 

Usually, the decrease in conductivity during chemisorbtion of alkyl radicals on semiconductor oxides of n-type at elevated temperature has a reversible nature. However, the effect value under the same conditions depends on the chemical nature of adsorbent. For example, the following adsorbent activity row can be deduced if the oxides being studied are arranged in a chemisorbtion-induced conductivity descent order. In case of, say, CH2-radicals, the other experimental conditions being the same, we obtain ... 

Knowledge of the nature of adsorbed residues which act as a poison to the catalyst... 

The question now arises of what simplification is possible in the treatment of orientationally structured adsorbates and what general model can be involved to rationalize, within a single framework, a diversity of their properties. Intermolecular interactions should include Coulomb, dispersion, and repulsive contributions, and the adsorption potential should depend on the substrate constitution and the nature of adsorbed molecules. However difficult it may seem, all these factors can be taken into account if we follow the description pattern put forward in this book. Its fundamentals are briefly sketched below. 

Much of the early work on the nature of adsorbents sought to explain the equilibrium capacity and the molecular forces involved. Adsorption equilibrium is a dynamic concept achieved when the rate at which molecules adsorb on to a surface is equal to the rate at which they desorb. The physical chemistry involved may be complex and no single theory... 

N(ls) spectra have provided very clear evidence for the nature of adsorbed ammonia and hydrazine (47-47c, 52, 64) whether adsorption is molecular, or if dissociated, the extent of the dissociation, i.e., whether the surface species are NH2, NH, or N. 

Chemical nature of adsorbant can be varied so that it is selective for a particular functional group in the analyte Emulsions are not formed between the two phases... 

The reaction pathway, reactivity of the active sites, and the nature of adsorbed intermediates constitute the catalytic reaction mechanism. Our study has been focused on the investigation of the nature of adsorbed intermediates under reaction conditions. We report the results of in situ infrared study of CO and ethanol oxidation on Au/Ti02 catalysts. This study revealed the high activity of Au/Ti02 is related to the presence of reduced Au and oxidized Au sites which may promote the formation of carbonate/carboxylate intermediates during CO oxidation. 

Thermst-Desorpaon-Spectroscopy (TDS) Heel Desorbed atoms and molecules Nature of adsorbed species > Thermodynamics of adsorption / desorption processes... 

A still more complete insight into the nature of adsorbed species can be obtained from experiments (I) on thermionic emission, ( ) with the field emission microscope, and (S) with the ion gauge. From some thermionic experiments, particularly with cesium adsorbed on tungsten, it is learned that (a) Cs can be adsorbed as positive ions as well as adatoms (b) as the concentration of adsorbed cesium increases, the ratio of adions to adatoms decreases (c) the forces produced by adions are long-range forces which have appreciable effects over distances of 10 to 20 atom diameters (d) adatoms and adions can migrate over the surface at much lower temperatures than those at which they evaporate from the surface. 

The nature of the methanol-zeolite interaction has been shown to be sensitive to a number of parameters and as such has proved to be a good benchmark for judging the reliability of quantum chemical methods. Not only are there a number of possible modes whereby one and two molecules interact with an acidic site (245), the barrier to proton transfer is small and sensitive to calculation details. Recent first-principles simulations (236-238) suggest that the nature of adsorbed methanol may be sensitive to the topology of the zeolite pore. The activation and reaction of methane, ethane, and isobutane have been characterized by using reliable methods and models, and realistic activation energies for catalytic reactions have been obtained. 

In that case bromine was the migrating species. The better correlation with cr+ rather than [Pg.584]

Clearly a set of monoclonal antibodies may help elucidate the nature of adsorbed protein orientation and conformation. Such studies are in progress by several groups. 

Johannson et al. [21] investigated the nature of adsorbed silane coupling... 

Studying the amount adsorbed and the nature of adsorbate/solid interactions applies primarily to the S/G and S/L interfaces. Adsorption is the... 

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