The Use of a Continuous Function

The requirement that E is continuous function of q means that, in the limit, point heterogeneity (or one site per element ds) is assumed. Hence, at any time, there is a Maxwellian distribution of probabilities for adsorption on all sites with the maximum probability centered at Et. We now examine the effect of such a distribution on rates of desorption in view of the fact that thermal desorption techniques are frequently being employed to obtain information about the distribution of site energies and about the different adsorbed states on an adsorbent surface. 

We first assume a surface comprising homogeneous patches and a constant distribution of activation energies for desorption among the patches. For the a th patch, the rate of desorption at a constant temperature T for a first-order process is given by 

From Eq. (23), with 0 as a continuous function of E, the relation between 9 and E for increasing times 0, is shown in Fig. 1, where 

The total bare surface at time t is then given by 

SO that the profile varies with rise of temperature. Consequently the amount desorbed, which for a constant profile is linearly related to the temperature, increases more rapidly. 

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