The physisorption of CH4 on graphite and on a (9,0) carbon nanotube

Our best estimates for the binding energy of methane on graphite, on a (9,0) single-walled carbon nanotube (SWCNT) and at the groove site between two (9,0) SWCNTs are 3.5 ± 1, 2.9 ± 1, and 5.6 ± 1 kcal/mol, respectively. Our computed values are in good agreement with the available experimental values. The calculations, therefore, support the current view that methane initially fills the groove site and then covers the outer nanotube surfaces, and that the binding energy of graphite is intermediate between the binding energy values for these two nanotube binding sites. In turn, the experimental results support the use of a cluster model in conjunction with the MP2 level of theory for the study of molecules that are weakly bound to SWCNTs.