We have studied the bonding of N-2 to a (9, 0) carbon nanotube using the MP2 and ONIOM methods with extended basis sets. We find a weak dispersion type bond with the N-2 similar to3.3 Angstrom away from the surface. Our best estimate of the binding energy, including the effect of expanding the high accuracy piece from ethylene to cluster A. is 1.88 kcal/mol for bonding in a twofold site and 1.97 kcal/mol for bonding in a sixfold site. We find N-2 is bound more strongly to a graphitic surface by similar to0.3 kcal/mol. (C) 2003 Elsevier Science B.V. All rights reserved.