Desorption measurements

The flash desorption technique is applied usually in ultrahigh vacuum conditions. Then all the mentioned contributions to S and F should be accounted for in the evaluation of the experimental desorption curves. The effect of Sw on the results of desorption measurements is discussed in... 

Figure 7.7. Temperature-programmed desorption measurements corresponding to zero-, first-, and second-order kinetics of silver from ruthenium, CO from a stepped platinum surface, and N2from rhodium, respectively (data adapted from [J.W. Niemantsverdriet,...

Fig. 1.6. Thin layer cell for in situ IR absorption-desorption measurements based in a model proposed by Seki et al. [32]. WE = working electrode, W = window, L=lead, M = micrometer screw, S = steel spring, SM = simmer gasket.

Shumaker Parry, J. S. Campbell, C. T., Quantitative methods for spatially resolved adsorption/desorption measurements in real time by surface plasmon resonance microscopy, Anal. Chem. 2004, 76, 907 917... 

Correlations between surface species and emitted secondary ions are based on characterization of the surface adlayer by adsorption and thermal desorption measurements. It is shown that the secondary ion ratios RuC+/Ru+ and R CTVRuJ can be quantitatively related to the amount of nondesorbable surface carbon formed by the dissociative adsorption of ethylene. In addition, emitted hydrocarbon-containing secondary ions can be directly related to hydrocarbon species on the surface, thus allowing a relatively detailed analysis of the hydrocarbon species present. The latter results are consistent with ejection mechanisms involving intact emission and simple fragmentation of parent hydrocarbon species. 

Adsorption and Thermal Desorption Measurements. In order to correlate emitted SIMS ions with the identity of various surface species formed by the ethylene/Ru(001) interaction, we first characterize the resulting adlayer by adsorption and thermal desorption measurements. 

Thermal desorption measurements were carried out by first exposing the clean surface to a 15 L dose of ethylene at 323 K. 

Ens, W. Mao, Y. Mayer, F. Standing, K.G. Properties of Matrix-Assisted Laser Desorption. Measurements Wifli a Time-to-Digital Converter. Rapid Commun. Mass Spectrom. 1991, 5, 117-123. 

Anion Desorption Measurements. Reactive scattering by DEA fragment ions in condensed media was first noted in the form of OH electron-stimulated desorption (ESD) yields from O2 embedded in multilayer alkane films [246] and subsequently for aniline physisorbed on top of O2 solids [215]. The anion produced following DEA to N2O has also been observed to react with other N2O molecules within an Ar/N20 matrix to generate a desorbed yield of NO and NO2, among other products. Part of the H2 ESD yield observed from multilayer films of H2O, at incident electron energies below 10 eV, has also been attributed to proton abstraction by fragments produced by DEA, viz., -I- H20 H30 ... 

The thermal conductivity (TC) detector consists of four filaments embedded in a stainless-steel or brass block which acts as a heat sink. The TC detector is extremely sensitive to temperature changes and should be insulated to prevent temperature excursions during the time in which it takes to complete an adsorption or desorption measurement. Long-term thermal drift is not significant because of the calibration procedure discussed in the next section and therefore, thermostating is not required. 

In solid states, cohesive energy is usually derived from a thermodynamic measurement, such as the temperature dependence of the vapor pressure of a solid. In surface science, the binding energy is usually derived by a temperature programmed thermal desorption measurement. Most of these measurements are done at high temperatures where... 

At sufficiently low Ts 100 K, Ar residence times on the surface are sufficiently long that trapping-desorption measures desorption from a fully equilibrated Ar on the surface. In this case, measurements of Df(Ef, 6f, Ts) showed that (Ef) <2kBTs and D f(0f) is broader than cos 6f, i.e., somewhat different than the usual equilibrium assumptions [138]. However, these results are fully consistent with detailed balance and the , and 6t dependence observed for a(E, Qt, Ts) [32,138]. 

Abiotic soil desorption measurements are probably the most important tests to precede measurement of microbial degradation. Desorption tests measure the site-specific soil/water partition coefficients for the contaminants of interest. Several experimental protocols are available for measuring partition coefficients (Wu Gschwend, 1986 Rogers, Tedaldi Kavanaugh, 1993). At the two extremes of bioavailability and biodegradability, contaminants can either be detected near their solubility limit or can be undetectable in the aqueous phase. Measurements of aqueous phase and soil phase concentrations in equilibrium may... 

Hydrogen and water desorption measurements indicated that only the a-Fe203 (0001) face can dissociate hydrogen, which then reacts with lattice oxygen to form water, thereby reducing the oxide film. This result highlights the role of water in the catalytic dehydrogenation of ethylbenzene. Water not... 

Product state analysis offers a flexible way to obtain detailed state resolved information on simple surface reactions and to explore how their dynamics differ from the behaviour observed for H2 desorption [7]. In this chapter, we will discuss some simple surface reactions for which detailed product state distributions are available. We will concentrate on N2 formation in systems where the product desorbs back into the gas phase promptly carrying information about the dynamics of reaction. Different experimental techniques are discussed, emphasising those which give fully quantum state resolved translational energy distributions. The use of detailed balance to relate recombinative desorption measurements to the reverse, dissociation process is outlined and the influence of the surface temperature on the product state distributions discussed. Simple low dimensional models which provide a reference point for discussing the product energy disposal are described and then results for some surface reactions which form N2 are discussed in detail, emphasising differences with the behaviour of H2. 

With simple probe molecules, such as H2, information about the number of surface metal atoms is readily obtained by using adsorption measurements. However, even with such simple probe molecules further information about the heterogeneity of a surface may be obtained by performing temperature-programmed desorption measurements. With probe molecules which are chemically more specific (e.g., NH3 and organic amines, H2S and organic sulfides) it may be possible to obtain information about the number and nature of specific types of surface sites, for example, the number and strength of Lewis or Bronsted acid sites on oxides, zeolites or sulfides. 

The data shown here for diffusion refer to the system polyethyl acrylate-benzene, and have been determined by Kishimoto and Enda (unpublished) by using the sorption technique. Values of D calculated from both absorption and desorption measurements agreed with each other over the range of benzene concentration studied at each temperature of the experiment, and the D0 values were determined by appropriate graphical extrapolation of those D values. In Fig. 15 are shown... 

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