The long-range interactions between the atoms and diatoms in their ground and first excited states as they appear as fragments on the water dissociation have been modeled. The computed long-range coefficients, which are function of the interaction angle and the interatomic distance of the diatomic, are used to build potential energy functions to represent the long-range energies within this system. (C) 2003 Elsevier Science B.V. All rights reserved.