MONTE CARLO CALCULATIONS FOR THE INTERACTION OF 12-6 ARGON AT 80 K WITH GRAPHITE IN THE REGION OF MONOLAYER ADSORPTION

The grand ensemble Monte Carlo method has been used to simulate the adsorption of 12-6 argon on a graphite substrate with periodically varying adsorbate-adsorbent potential at 80 K. The grand ensemble method enables stable and metastable States to be distinguished although these may be ergodically separate. The results of these calculations and those carried out earlier for a continuum model, represented by a 9-3 potential, have been compared with experimental data. Experimental isotherms appear to be in better agreement with the continuum results than with those for the periodic potential. Isosteric heat curves on the other hand were in satisfactory agreement with experimental data for coverages of up to a monolayer but showed marked deviations beyond this point. Tests of theoretical models were restricted to an appraisal of the zero coverage region and of the Hill-de Boer isotherm in its original and modified forms. The latter was in poor agreement with MC data