Moderate coverage

Enhanced excimer emission was also observed from PBAC bound to a-ZrP [20], Excimer formation from pyrene is well known in aqueous solutions [54], As in the case with AMAC, excimer formation is increased with PBAC concentration (Fig. 16) due to increased local concentrations but with two significant differences. Hydrophobic interactions between the pyrene molecules favor the aggregation of PBAC even at moderate coverages and the PBAC singlet excited state is much longer lived ( 200 nsec) than that of AMAC ( 10 nsec) these factors, in turn, promote excimer formation even at low loadings. The broad, red-shifted fluorescence band with a peak centered around 470 nm, characteristic of the pyrene excimer emission, is evident in Fig. 16. Rapid formation of the excimer at low coverages is also evident from the plot of the ratio of emission intensities at... 

Many adsorption systems can be shown to correspond either to a localized adsorption model or to a two-dimensional gas. However, there must also be a large number of adsorbate-adsorbent pairs for which the potential energy functions will have variations intermediate between the extremes required for the limiting models. The formal equations applicable to these systems are included in the theory presented here, and furthermore, it appears to be feasible to carry out specific computations of the isotherms and heats for such systems up to moderate coverages (11, 24). 

The analysis of the shape of the heat emission peaks in the above studies indicated that peaks typical of fast chemisorption processes became more asymmetric for moderate coverages. This indicated that an activated process started at those coverages superimposed on a nonactivated step. IR spectroscopy verified this conclusion. Della Gatta et at. (112) showed that such a peak can be deconvoluted by subtracting from it a peak of the same height from the second adsorption run for which the adsorption is reversible. 

For values of Ka Pa near 1, i.e., at moderate coverages, the complete equation (3.21) must be used. Alternatively, the Freundlich isotherm (3.23) can be used. 

Evaluation of spectroscopic data and ionic-strength dependence to guide the selection of divalent cation sorption reactions at low to moderate coverage where mononuclear sorption is the dominant reaction process. 

Consider acUiorbates which cover one tenth of their 10 cm phj i-cally identical sites on a catalyst, as one would say of moderate coverage. The thickness of the surface phase ought to be of the order of magnitude of 10 cm in consistence with the number 10 cm of sites. The three-dimensional concentration of the adsorbates in the surface phase is now 10 X 0.1/10 = 10 cm , which is comparable to that of liquid molecules. The system of an elementary reaction consisting of an adsorbed species could hardly be statistically independent of surrounding adsorbates any more than a liquid molecule is from the surrounding ones. 

Substituting Eq. (2.12) into Eq. (2.9), we get Temkin isotherm with moderate coverage ... 

The fourth hypothesis of Temkin. To evaluate the integral in (2.146), Temkin put forward the fourth hypothesis that the concept of the moderate coverage, and also that of concerning the limits uq and ui. The moderate coverage refers to that almost sites are occupied for the most active adsorption area, but the most inactive adsorption area is almost completely empty on a non-uniform surface. It is assumed that for the upperior limit of t, all active sites are occupied. This means ... 

---