A highly accurate potential energy surface (PES) for the ground state (1(2)A') of the title reaction has been computed using an ab initio multireference configuration interaction method (MRCI) with Davidson correction and a large orbital basis set (aug-cc-pv5z). The many-body expansion and neural network method have been used to fit a set of 10 190 ab initio points. The new potential energy surface has a root-meansquare (rms) error of 0.095 kcal/mol. The total integral reaction cross-sections have been calculated as functions of the collision energy in the range of 0-2.0 eV by means of the quasi-classical trajectory calculation (QCT). (C) 2008 Published by Elsevier B.V.