Abstract
A model in which the atoms in the second layer of a monolayer-plus helium film are assumed to form a quasi-two-dimensional gas is used to analyze the isotherm data of Goellner, Daunt, and Lerner for helium on Grafoil. The parameters in the model are determined by a least-squares fit of the model isotherm to the data. These parameters include the second and third virial coefficients of the quasi-two-dimensional gas and the binding energy of the second-layer atoms to the first layer. The empirical values are compared to recent theoretical predictions for the two-dimensional helium gas. The agreement and discrepancies between theoretical and empirical values are discussed. The conclusion is that the second layer (at low densities) can be described as an imperfect two-dimensional gas with perhaps some modification of the interatomic potential due to substrate effects.
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Work supported, in part, by a grant from the National Science Foundation.
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Novaco, A.D. A virial coefficient analysis of helium adsorption isotherms. J Low Temp Phys 21, 359–368 (1975). https://doi.org/10.1007/BF01141332
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DOI: https://doi.org/10.1007/BF01141332