[en] This study of H₃^- employs a valence-configuration-interaction (VCI) wavefunction expansion with a double-zeta-plus-polarization-and-diffuse-orbital Slater-type orbital (STO) basis set. Calculations have been carried out for both triangular and linear geometries to define the lowest singlet potential energy surface (PES). It is found that the minimum energy reaction path corresponds to a linear conformation of H^- + H₂. The calculated barrier height is 15 kcal/mol which is close to that obtained using a similar quality basis set. The energy contours for the isosceles triangle arrangement of nuclei indicates that the least energy path leads to dissociation into H^- + H + H. A threshold of approximately 1 eV and a maximum in the exchange cross section between 2 and 3 eV collision energy are found