As desorption

Femtosecond lasers represent the state-of-the-art in laser teclmology. These lasers can have pulse widths of the order of 100 fm s. This is the same time scale as many processes that occur on surfaces, such as desorption or diffusion. Thus, femtosecond lasers can be used to directly measure surface dynamics tlirough teclmiques such as two-photon photoemission [85]. Femtochemistry occurs when the laser imparts energy over an extremely short time period so as to directly induce a surface chemical reaction [86]. 

An electron or photon incident on a surface can induce an electroiuc excitation. When the electroiuc excitation decays, an ion or neutral particle can be emitted from the surface as a result of the excitation. Such processes are known as desorption induced by electroiuc transitions (DIET) [82]. The specific teclmiques are known as electron-stimulated desorption (ESD) and photon-stimulated desorption (PSD), depending on the method of excitation. 

For each group of pores, the pore volume 6v is related to the core volume by means of a model, either the cylinder or the parallel-sided slit as the case may be. Allowance is made for the succession of film thicknesses corresponding to the progressive thinning of the multilayer in each pore, as desorption proceeds. Thus for group i, with radius rf when the film thickness is tj j > i) and the core volume is the pore volume 6vf will be given by... 

In order to allow for the thinning of the multilayer, it is necessary to assume a pore model so as to be able to apply a correction to Uj, etc., in turn for re-insertion into Equation (3.52). Unfortunately, with the cylindrical model the correction becomes increasingly complicated as desorption proceeds, since the wall area of each group of cores changes progressively as the multilayer thins down. With the slit model, on the other hand, <5/l for a... 

The situation changes when the system pressure becomes high enough for refrigerant to condense in the condenser and reject the resulting latent heat to the environment. Further addition of heat to the adsorbate desorbs more refrigerant which condenses in the condenser and trickles down into the receiver. The system pressure stays approximately constant as desorption and condensation proceed. 

In this work the methanol and methyl iodide conversion and their co-reaction are investigated on Fe-Beta zeolite without any oxygen. Partly Fe-ion-exchanged Beta-300 i.e. Fe-H-Beta-300 (shortly Fe-Beta-300) zeolite keeps the light acidity to a certain extent, however the presence of Fe ions (as transition metal, Fe is an excellent Lewis acid) can modify the reaction pathway. This Fe-Beta-300 has been tested already by low temperature peat pyrolysis [6], At present, the adsorption as well as desorption of methanol are followed-up by radiodetectors using ( -radioisotopic labeling [4, 7]. The... 

Sorption in the environment encompasses adsorption/absorption as well as desorption. The former depends on both physico-chemical... 

Cl in conjunction with a direct exposure probe is known as desorption chemical ionization (DCI). [30,89,90] In DCI, the analyte is applied from solution or suspension to the outside of a thin resistively heated wire loop or coil. Then, the analyte is directly exposed to the reagent gas plasma while being rapidly heated at rates of several hundred °C s and to temperatures up to about 1500 °C (Chap. 5.3.2 and Fig. 5.16). The actual shape of the wire, the method how exactly the sample is applied to it, and the heating rate are of importance for the analytical result. [91,92] The rapid heating of the sample plays an important role in promoting molecular species rather than pyrolysis products. [93] A laser can be used to effect extremely fast evaporation from the probe prior to CL [94] In case of nonavailability of a dedicated DCI probe, a field emitter on a field desorption probe (Chap. 8) might serve as a replacement. [30,95] Different from desorption electron ionization (DEI), DCI plays an important role. [92] DCI can be employed to detect arsenic compounds present in the marine and terrestrial environment [96], to determine the sequence distribution of P-hydroxyalkanoate units in bacterial copolyesters [97], to identify additives in polymer extracts [98] and more. [99] Provided appropriate experimental setup, high resolution and accurate mass measurements can also be achieved in DCI mode. [100]... 

API offers unique opportunities for the implementation of new sources or to develop new applications. Atmospheric pressure matrix assisted laser desorption (AP-MALDI) [21] can be mounted on instruments such as ion traps which were originally designed only for electrospray and LC-MS. New API desorption techniques such as desorption electrospray (DESI) [22] or direct analysis in real time (DART) [23] have been described and offer unique opportunities for the analysis of surfaces or of solid samples. 

Absorption of Butadiene by Cyanocobaltate(II). Of the various substrates reduced by this catalyst system, butadiene was especially convenient for use as a model substrate in a study of mechanism, since its absorption, as well as desorption of product butenes, could be readily followed using a gas buret, and the products formed were easily analyzed by vapor phase chromatography. 

Method. In the steady state the first-order rate law — d In AT/dt = kg is obeyed (8, 29). Experimentally one follows the change in total film area (AT) as desorption proceeds while maintaining a constant ir. The apparatus (Figure 1) is essentially the same as previously used (8) but modified to maintain automatically a constant tt, while recording changes in At owing to desorption. 

Since T ASr is generally quite negative, the entropy term favors the reverse process, such as desorption from the surface into the gas. 

Numerous industrial operations involve a heat transfer between a liquid phase and a gaseous phase, with an important mass transfer effect, either as desorption-evaporation or as absorption-condensation. Here are some examples reconcentration, by evaporation, of solvents, toxic industrial effluents production, by absorption, of industrial aqueous acid solutions reversible or irreversible chemical reactions (oxidation, hydrogenation, sulfonation) purification of permanent gases (air, smoke) by scrubbing of soluble vapors desorbers and absorbers for heat pumps, where these two operations occur simultaneously. 

Delivery or secretion of the diffused material through the polymer interface, also known as desorption. 

The temperature dependence of S0 measured at normal incidence and Ex = 0.39 eY is reported in Fig. 11 for Ag(2 10) ( ) and compared with the behaviour observed at the same E and 0 for Ag(l 0 0) (dashes) and Ag(l 1 0) (solid line) at the same E and 0. The data for Ag(41 0) are reported, too ( , O, x) for two different 0, corresponding to similar values of S0. We notice that all surfaces show a smooth T dependence except for Ag(l 0 0), for which S0 drops abruptly beyond T = 170 K [100], i.e. as soon as desorption from the molecular well becomes important over the time scale of the experiment (0.3 sec). The Ag(4 1 0) and Ag(l 1 0) curves have the same behaviour up to 350 K, at which temperature S0(T) becomes steeper for Ag(41 0). Such difference is due to the dissociation process, which occurs only at steps for Ag(41 0) and takes place at regular sites for Ag(l 1 0). When the lifetime in the chemisorbed precursor becomes shorter than the time needed to search for the defect, the dissociation probability for Ag(41 0) decreases more rapidly with respect to a situation where no searching for an active site is necessary. The S0(T) curve of Ag(2 10), on the other hand, nearly perfectly overlaps with the one of Ag(l 1 0). The decrease of S0(T) on Ag(2 1 0) tells us further that the dissociation mechanism is mediated also in this case by a short lived molecular precursor, which has the choice between desorbing and dissociating. 

As shown in Figure 6.7, partitioning between the aqueous and solid phases may result from absorption, adsorption/desorption, and sedimentation processes. The contaminant may be taken up into the interior of a solid by means of diffusion in a process known as absorption. As previously described in air-solid partitioning, the contaminant may also be taken up by the surface of the solid, known as adsorption, and its release from the surface of the solid is known as desorption. Adsorption of a chemical to soil or sediment particles may be a result of electrostatic or hydrophobic attraction between the contaminant and the solid surface.23 Once associated with solid particles, the contaminant may also settle to the sediment surface. This process, known as sedimentation, typically occurs in water bodies with laminar flow, such as a wetland. The increase in contaminant concentration in the solid phases as a result of any of these partitioning processes is known as accumulation.14... 

Properties of relevance for hydrogen storage applications, such as desorption enthalpies and weight and volume efficiencies, are summarized in Table 21. 

Although partial oxidation of Co by protons at temperature lower than 723 K could not be excluded, the H2 evolution in the temperature range of 470 to 770 K can be considered as desorption of activated H2 on Co in Pt-Co bimetallic particles. 

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