Accurate double many-body expansion potential energy surface for N3((4)A'') from correlation scaled ab initio energies with extrapolation to the complete basis set limit.

A new global potential energy surface is reported for the (4)A'' ground electronic state of the N(3) system from double many-body expansion theory and an extensive set of accurate ab initio energies extrapolated to the complete basis set limit. It shows three equivalent metastable potential wells for C(2v) geometries that are separated from the three N((4)S) + N(2) asymptotes by energy barriers as predicted from previous ab initio work. The potential well and barrier height now predicted lie 42.9 and 45.9 kcal mol(-1) above the atom-diatom dissociation limit, respectively, being about 1 kcal mol(-1) lower than previous theoretical estimates. The ab initio calculations here reported predict also a (4)B(1)/(4)A(2) conical intersection and reveal a new minimum with D(3h) symmetry that lies 147 kcal mol(-1) above the atom-diatom asymptote. All major topographical features of the potential energy surface are accurately described by the DMBE function, including the weakly bound van der Waals minima at large atom-diatom separations.