Here, since the volume of the pore is fixed, and conditions are isothermal, we assume that pressure is adjusted by increasing the amount of CO 2 in the pore. Since the predicted well depth exceeds thermal energies at the temperature in question, we hypothesize that CO 2 particles begin to scatter out of the outer potential band when the mean free path for particle-particle scattering reaches some critical value λ c . From elementary kinetic theory, we know that this mean free path is inversely proportional to the gas concentration so that we can write