is small compared to 
, the energy barrier separating adjacent sites. The adsorbate has little chance of migrating to neighbouring sites and such adsorption is necessarily
localized.
Source:
PAC, 1976, 46, 71
(Manual of Symbols and Terminology for Physicochemical Quantities and Units - Appendix
II. Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Part II:
Heterogeneous Catalysis)
on page 76