Chemical equilibria, high pressure spectroscop

A second type of adsorption is called chemisorption. In this case, the adsorption energy is comparable to the chemical bond energies and adsorbate molecules have the tendency to be localized at particular sites even though surface diffusion or some molecular mobility may still occur. Due to the chemical nature of the interactions between the gas and the solid surface, the equilibrium gas pressure in the adsorption system can be extremely low. This enables one to study the adsorbent-adsorbate system under high vacuum using diffraction and spectroscopic techniques for the identification of the actual species presented on the surface and the determination of their packing and chemical state. 

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