Melting and Evaporation of Monolayer H2-D2 Mixtures Adsorbed on D2-Plated Graphite

We report heat capacity measurements on second layer mixtures of H2-D2adsorbed on exfoliated graphite plated with one monolayer of D2, for 3K<T<15K, 2nd layer coverages between 0.3 and 0.44 layers, and x, the D2concentration, between 0 and 1, across the three-phase melting region (Tm) and the two-phase liquid-vapor coexistence region through its high temperature boundary (Te). Deviations from a linear dependence of Tmand Teon x have been found. An estimate of the degree of fractionation is presented.