Physical Adsorption of Argon and Nitrogen on Graphite

In this experiment you will record an adsorption isotherm of N2 molecules and a second one of Ar atoms on a graphite substrate at a temperature of 77.4 K. A feature of the N2 isotherm cor-responding to a known density of molecules on the graphite substrate allows one to calculate the total substrate area. With the substrate area thus determined, the Ar isotherm can be used to determine the density of Ar atoms at single (mono)layer completion, allowing for a determina-tion of the monolayer Ar-Ar spacing. This number can then be compared to the known nearest neighbor spacing of Ar atoms in the solid 3-D phase, and the Ar-Ar separation derived from the Lennard-Jones potential.