Abstract:
From adsorption isotherms of krypton on graphite measured between 79.24 and 88.46 K. in the
monolayer domain a two-dimensional triple point of 84.8 ± 0.5 K is determined for this system.
Thermodynamic analysis of these isotherms and of the isotherms of xenon on graphite measured by
Thomy and Duval suggests that the surface structure plays a prominent role in the formation of
dense monolayers on the (0001) face of graphite. To explain the striking difference of behaviour
of the two rare gases, two factors have to be taken into account; the height of potential barriers to
translation and dimensional incompatibility between the lattices of the bulk adsorbates and of the
(0001) face of graphite, the first “solid ” layer appearing being in registry with the substrate. A
single isotherm of argon on graphite measured at 68.78 K suggests that a more exhaustive study of the
Ar + graphite system could be useful in establishing the relative importance of both factors.
