ADSORPTION OF KR AND CH4 ON N-HEXANE-PREPLATED GRAPHITE - DISPLACEMENT OF AND LAYERING ON THE CONDENSATE

Adsorption of Kr and CH4 on graphite preplated with n-hexane has been studied volumetrically at 77 K. Both gases undergo layering transition s not only on the graphite surface but also on the n-hexane layer. Eve n when more than one monolayer of n-hexane covers the surface, the lay ering occurs on the graphite surface, indicating that Kr and CH4 displ ace part of preadsorbed n-hexane. This is the first observation where both the displacement of and the layering on the preadsorbed condensat e occur in the same system, although the latter predominates. We exami ne the present systems as well as those studied previously in terms of the monolayer displacement energy of the adsorbate. We find that the monolayer displacement energy difference between the two co-adsorbates can successfully predict which of the two modes of coadsorption, the layer-on-layer mode and the two-phase mode, appears in the system. (C) 1997 Elsevier Science B.V.