A total of 3261 ab initio energies calculated at the RHF/MP2 level were used to obtain an analytical representation of the potential energy surface (PES) for the title reaction considering all the vibrational degrees of freedom. The analytical potential is constructed by switching three local representations of the PES utilizing a distance like function, and it reproduces well the ab initio energies up to 20 kcal/mol above the dissociation threshold with the root-mean-square (rms) deviation equal to 1.5 kcal/mol. Two types of classical trajectory studies, i.e., power spectra calculations and product-state distribution analysis, were pet-formed to assess the reliability of the present potential function. The results were found to be in good agreement with the available experimental ones. (C) 1997 American Institute of Physics.