On physical adsorption XVI. The physical interaction of H 2 , D 2 , CH 4 , and CD 4 with graphite

Abstract

The data of Constabaris, Sams & Halsey (1961) for adsorption of the isotopic pairs H 2 -D 2 and CH 4 -CD 4 by graphitized carbon black are interpreted in terms of a theory of the mobile adsorbed film, from which are deduced the potential energy of interaction between adsorbent and adsorbate and changes in translational, rotational and vibrational kinetic energies of the adsorbate molecules. These quantities are evaluated from the experimental data, and provide a description of the experimental adsorption isotherms and their variation with temperature: the results derived are compared and found to be in agreement with the thermodynamics of the process. The total adsorptive interaction for the systems considered is shown to result from two (and only two) contributions: the London-type dispersion forces between the adsorbate and the adsorbent, and the interaction due to the polarization of the adsorbate by the surface electric field. A calculation by Crowell & Steele (1961) of the dispersion force in­teraction between methane and graphite is found to be in excellent agreement with the value elicited from the experimental data by the present interpretation.