We have studied the reaction of N and 0 atoms with a (9,0) carbon nanotube using clusters and the ONIOM method with the B3LYP/6-31G* level of theory. For both N and 0 atoms in their ground state, addition to the CNT requires a surface crossing and presumably involves a barrier, while we show that addition of the excited state of N(D-2) has no barrier, and we believe this also to be true for O(D-1). Both N and 0 atoms bond in a bridged structure and have bond strengths of 25.0 and 67.9 kcal/mol (estimated), respectively, with respect to CNT plus the ground state of the N or 0 atom. (C) 2003 Elsevier Science B.V. All rights reserved.