Concave kinetic term

The permeation of a gas through a porous polymer is generally described by equations based on the kinetic theory of gases. The sorption isotherm described by Eq. 1 is concave to the pressure axis and is commonly observed for a penetrant gas in a glassy polymer. It is composed of Henry s law and Langmuir-terms [20] ... 

The kinetic Fn-I/FID and FID/DD isotope effects are about 5 at room temperature and are similar, i.e. follow the rule of the geometric mean (RGM) as predicted by Fig. 6.14(a). The total HH/DD isotope effect is about 25. Concave Arrhenius curves indicate tunneling at low temperatures. This finding has been interpreted in terms of a single barrier reaction where all H loose zero-point energy in the transition state. 

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