ion source (D − ) is used for the tokamak neutral beam injectors [32, 33]. Many studies have been devoted to the calculation of elastic and inelastic cross-sections for H$_{2}$-H − collisions and for all isotopologues, [11, 24, 34–45], most of them for energies significantly larger than 1 eV above the lowest dissociation limit H$_{2}$ + H − . However, at such energies the theoret- ical cross-sections may not be reliable: the dissociation energy of the H$_{3}$ ground state lies only 0.75 eV above the H − 3 dissociation energy, and the non-Born-Oppenheimer interaction between the ground states of H$_{3}$ and H − 3 could be significant. The non-Born-Oppenheimer interactions have been taken into account only in Ref. [46] within a reduced-dimensionality approach, where only linear geometries of H − 3 have been taken into account. Finally, the photodissociation of H$_{2}$D − has been studied in a simplified approach based on the Franck- Condon overlap between a bound level and a scattering state of H$_{2}$D − [47], since the ab initio dipole moments of H − 3 were not available at that time. The present study is mainly motivated by the formation of H − 3 bound states in low-energy collisions between H$_{2}$ and H − . In such collisions H − 3 can be formed only if a third body (other than H$_{2}$ or H − ) participates (three-body recombination – TBR) or if a photon is emitted (radiative association – RA). Both processes could be relevant for the chemistry of cold interstellar clouds, if H − is present [48]. Note that the H − ion has not been detected so far in the interstellar medium (ISM): it cannot be directly observed by usual photoabsorption spectroscopy because H − has only one bound electronic state. The evaluation of the cross-section for radiative association of H$_{2}$ and H − at low energy (10-30K) requires an accurate PES with a precision around 1 cm − 1 or better, and permanent dipole moment surfaces (PDMS) for H − 3 . In the present study we calculated a new ab initio PES for the H − 3 electronic ground state on a dense and large grid for internal coordinates, using a larger electronic basis set than those of PES-SM and PES-PS calculations. Special care is taken in order to account for the long-range behavior of the surface. We also obtain for the first time the PDMS of the H − 3 electronic ground state. We constructed Fortran subroutines that calculate PES and PDMS values for any arbitrary geometry using B-spline interpolation procedures, and we determine the bound states of H − 3 and D − 3 . The RA reaction will be treated in a separate study. The article is organized in the following way. In the next section, we discuss the calcu- lation of the new PES and the interpolation procedure. In Section III we compare the new PES with the PES from previous studies. Section IV is devoted to the calculation of bound 3