An Analysis of Physical Adsorption Isotherms in Ultrahigh-Vacuum Range

The detailed mechanism of physical adsorption was studied by use of the statistical theory of imperfect gases. The Kirkwood—Muller potential was used for the gas–solid interaction. Adsorption isotherms computed from both the classical method (high-temperature case) and the quantum-mechanical method (very low-temperature case) are given. In the case of the quantum-mechanical method of solution, the important portion of the Kirkwood–Muller potential is approximated by a linear potential, the Schrödinger equation is solved in terms of Bessel functions, and the eigenvalues of the energy are obtained. Comparisons of present results with Hobson's measurements (He on Pyrex glass at 4.2 °K and $N2$ on Pyrex glass from 63.3 ° to 90.2 °K) show that the present theories are adequate in the ultrahigh-vacuum range and suggest that physical adsorption of helium on Pyrex glass at 4.2 °K is completely quantized.