Kinetics of atomisation under stationary conditions when molecular adsorption is unactivated

3 Kinetics of atomisation under stationary conditions when molecular adsorption is unactivated 

We have already seen that atomisation experiments are designed to prevent the atoms produced by the surface ever returning there. This is done either by trapping the atoms at the walls of the apparatus, or by pumping them away, having tried to eliminate the possibility of their prior 

The constant surface coverage characteristic of any particular stationary condition can be identified with a corresponding equilibrium state in an isothermal system with partial pressures P1 and P2 as discussed in the previous paragraph. Accordingly, we substitute eqn. (33) into eqn. (36) to obtain 

This equation relates the equilibrium pressure (P2 ) of molecular gas in the hypothetical isothermal system which is necessary to achieve the same surface concentration of adsorbate as prevails during the practical atomisation experiment with an observable pressure P2, but it contains nothing which would enable that concentration to be calculated. 

Rather than consider the absolute rate of atomisation, it is sometimes more convenient to employ a parameter which expresses the efficiency of the process in terms of the probability that a molecular collision with the surface results in the atomisation of the molecule involved. Such a parameter is, a defined by the relation 

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