  The van der Walls interaction between a carbon nanotubes sheet (CNTS) and a
rare gas atom, is studied using both atomistic and continuum approaches. We
present analytical expressions for the van der Waals energy of continuous
nanotubes interacting with a rare gas atom. It is found that the continuum
approach dose not properly treat the effect of atomistic configurations on the
energy surfaces. The energy barriers are small as compared to the thermal
energy, which implies the free motion above the CNTS in heights about one
nanometer. In contrast to the energy surface of a graphene sheet, the honeycomb
lattice structure in the energy surface of a CNTS is imperceivable. Defects
alter the energy surface which therefore influence the gas absorbtion
mechanism. (Corresponding<EMAIL_ADDRESS>