THE INTERACTIONS OF NITROGEN MOLECULES ADSORBED ON GRAPHITE

Rksumk.- Les succ6s obtenus lors du traitement thkorique des interactions gaz rares-graphite et N2-N2 permettent d'Ctablir un modkle d'interaction mol6culaire de N2 avec le graphite. La forme non sphkrique de cette molCcule est introduite dans le calcul de I'Cnergie gaz-solide. De plus, I'interaction entre paires de molCcules N2 adsorbkes fait intervenir 1'Cnergie quadripolaire et la non-sphkricitk. Les Cnergies calculCes sont en bon accord avec celles obtenues B partir des chaleurs d'adsorption expCrimentales. On en dCduit les valeurs des barrikres de rotation et translation sur la surface. Ces valeurs permettent de caractkriser les Ctats de mouvement dans certaines des phases dCcouvertes rkcemment dans ce systkme. Abstract.- A model for the molecular interaction of N2 with graphite is proposed which is derived from successful treatments of the energies of rare gases on graphite and of the N2-N2 interaction. The non-spherical shape of this molecule is explicitly taken into account in the gas-solid energy; in addition, the interaction of a pair of adsorbed N2 molecules includes the quadrupolar energy as well as non-sphericity. Calculated energies are in good agreement with estimates obtained from the experimental heats of adsorption. Barriers to rotation and to translation across the surface are estimated and used to characterize the states of motion in some of the recently discovered ordered phases in this system. 1. Introduction.- Sinc