Competition between desorption and

In many studies [3-13], this competition between desorption and dissociation from the trapped precursor state has been modeled as competing, parallel reactions, both having rate constants and activation energies of the Arrhenius form ... 

M/SC on many, in particular, polymer substrates the desorption of adatoms should be taken into consideration. In this case the probability of M/SC phase nucleation at PVD, usually designated as condensation coefficient C, is defined by a competition between desorption of adatoms and their irreversible fixing on a substrate surface. Irreversibility of M/SC atom fixing is provided either by its aggregation with other atoms or by immobilization on surface defect which can be surface steps, outputs of dislocations, vacancies, etc. [42],... 

Adsorption and desorption phenomena often actually take place at the electrode surface (Fig. 2). Generally, adsorption from solution is characterized by competition between solute and solvent molecules. The electrode-solution interface can thus be assumed to conform to the illustration in Fig. 3, where electroactive species are adsorbed through replacement of preadsorbed solvent molecules. 

The present technique offered a direct method of studying the competition between oxidation and desorption in respect to the removal of a film of adsorbed oxygen. As soon as the surface area had become stabilized, a typical adsorption of some 80 yg. of oxygen at 20° exhibited the behavior described as follows. 

In the oxidation of CH4 and CjHg, no inhibition by the reactant is operative, and initial conversion is higher near the reactor inlet, where favourable conditions for ignition are stabilized. This relationship between dynamic behaviour and adsortion-desorption properties, finds support in the literature. Site competition between hydrocarbons and oxygen has been recognized as a key point in the mechanism of catalytic oxidation [3] in the same study, a substantially different behaviour in catalytic combustion was reported for alkanes and ethylene, and this was related to the strong adsorption properties of the latter. 

Asua et al. [49] have developed a model for estimating k, taking into consideration the possible reactions in the aqueous phase as well as the competition between termination and desorption when a monomer radical enters a particle already containing a radical. For low values of n, the authors arrived at the expression ... 

Rate data have often been approximated in terms of simple powers of reactant concentrations or partial pressures, but more widely applicable rate equations were derived by Hinshelwood and others to take into account competition between reactants, and possibly intermediates and products, for active sites. The form of the best equation may provide some mechanistic guidance, but when the process is multistep, with desorption/readsorption of intermediates, the kinetics may be extremely complex. 

The decay of the fractional coverage with time is depicted by the equation corresponding to the GC in Fig. 8. The competition between diffusion and desorption kinetics is again conveniently represented by a kinetic zone diagram. This is shown in Fig. 8 together with the equations pertaining to each zone. 

Oberg KI, van Broekhuizen F, Fraser FU, Bisschop SE, van Dishoeck EF, Schlemmer S (2005) Competition between CO and N2 desorption from interstellar ices. Astrophys J Lett 621 L33-L36... 

Flash desorption of oligomers relies on kinetic competition between evaporation and thermal decomposition. Molecular ion signals from the MS have been used to determine the average molecular masses and distribution of oligomers, whereas expert systems can be used to establish mechanisms for the thermal degradation of polymers, e.g. to determine the relationships between polymer structure and the corresponding Py-MS spectra. 

The observation of negative apparent activation energy can most simply be interpreted in terms of the competition between the adsorption and desorption of methylacetylene on the surface. This qualitative explanation is illustrated in Figure 3, where the steady-state production of trimethylbenzene is compared with the TPD trace of methylacetylene. The fall off in steady state cyclotrimerization rate matches the tail of the desorption spectrum and illustrates the role of reactant desorption at higher temperatiu-es controlling the availability of alkyne monomers and thus the overall cyclotrimerization rate in this temperatime/pressure regime. 

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