We report the first results of a thermodynamic analysis of data for ^He adsorbed on Grafoil. The ^He-graphite binding energy is in excellent agreement with a prediction made on the basis of '^He-graphite atomic scattering data.

A new analysis is presented of the critical-point behavior of two-dimensional melting in the Kosterlitz-Thouless-Nelson-Halperin-Young theory. The analysis confirms the Kosterlitz-Thouless-Nelson-Halperin-Young critical-point exponent, v=O. 36963. . . , but also gives a criterion for its own range of validity amounting to t « 10,where t is the reduced temperature. Both results are confirmed by direct numerical computation, and it is shown that the corresponding range of correlation lengths is g+ » 10'3 lattice spacings. The implications of these results for experimental verification are discussed.

We calculate the size and energy of distortions of solid 3He and 4He monolayers produced by the periodic potential of a graphite substrate, as a function of relative orientation angle of the incommensurate adsorbate and substrate lattices, using experimental elastic parameters of the monolayers, Fourier components of the substrate potential obtained from atomic scattering, and a phenomenological treatment of adsorbate phonons. We also predict the restoring force against relative twist of the two lattices, a parameter needed in analyzing the melting transition.

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