Accurate double many-body expansion potential energy surface for triplet H3+.: I.: The lowest adiabatic sheet (a3Σu+)

We report on a global potential energy hypersurface for the lowest triplet state of H-3(+) based on the double many-body expansion (DMBE) method and ab initio data points of V5Z quality. These data points are represented with a root mean square deviation of only 3.46 cm(-1) in the energy region below the H-2(+)(X(2)Sigma(g)(+))+H(S-2) dissociation threshold and with less than 15 cm(-1) up to the three-particle breakup energy. As expected from a DMBE approach, all dissociation limits are represented accurately and are approached in a physically correct manner. (C) 2003 American Institute of Physics.