Classical Theory of Small Energy Accommodation Coefficients. Application to3He and4He on W

摘要

Some recent experimental data on the energy accommodation coefficients of the systems3Hesngbnd;W and4Hesngbnd;W are compared with the predictions of the classical theories of gasndash;solid interactions. For reasons which are explained, these data should provide a particularly good test of theory. The classical lattice theory of energy accommodation coefficients is generalized, using results from other theories, to take account of the threehyphen;dimensional nature of the gas; this generalization involves, for example, elimination of the assumption of normal, headhyphen;on encounters of gas atoms with surface atoms and consideration of the hopping of gas atoms at the surface. The gasndash;solid interaction potential is the recently proposed modified exponential repulsion, the use of which allows considerable simplification of the analysis. The assumption that accommodation coefficients are independent of solid temperature, allowing use of a lattice model at zero temperature, is retained and discussed at some length. The application to Hesngbnd;W allows the calculations to be simplified by means of a perturbation procedure which is valid only for small accommodation coefficients. Although there are some disappointing features, in view of the approximations still existing in the theory the comparisons made are satisfactory. For example, there are no grounds for concluding, on the basis of these comparisons, that a classical model is inadequate for dealing with the accommodation of Hesngbnd;W.