Implementation of a fast analytic ground state potential energy surface for the N(²D) + H₂ reaction

A new implementation for the potential energy surface of the 1²A" state of the N(²D)+H₂ reaction is presented. Based on a much larger set of ab initio data, the new energy surface is an improvement over an existing surface in several crucial aspects, including removal of unphysical small scale structures at large separations, elimination of erroneous interpolations for the linear H-N-H configurations, and better agreement with ab initio calculations, especially in three key stationary points corresponding to the C_2v minimum, the C_2v transition state, and the N-H-H linear barrier. The NEW PESS code, based on low-order spline reproducing kernels in terms of bond-order variables, increases the efficiency of evaluating the potential energy function by more than tenfold.