Heat capacity of the commensurate phase and ordering transition of para-H2monolayers on graphite

Heat-capacity data for the √3 × √3 R30° commensurate-solid phase and commensurate ordering transition of para-${\mathrm{H}}_2$ monolayers on graphite show striking similarities to He monolayers. The commensurate-solid disordered-fluid phase boundaries have similar shapes and the transitions show similar critical behavior. A value of 0.36±0.05 is observed for the critical exponent α. At low temperatures the commensurate-solid phase behaves like an Einstein solid with a characteristic temperature of 53.4±1.2 K.