VI. SUMMARY AND CONCLUSIONS In the present study we have obtained the accurate potential energy surface and compo- nents of the permanent dipole moment for the H − 3 van der Waals molecule. The surfaces were calculated on a dense grid of geometries that covers short, intermediate, and long-range regions. In total, the ab initio calculations were made for 3024 geometries. The large basis and grid used in the calculations allows us to suggest that the obtained PES is more accurate than the results of the previous study [10, 11]. Comparison of the long-range behavior of the obtained PES with the expected analytical behavior of the PES confirms this conclusion. No previous data on the dipole moment of H − 3 is available. The obtained ab initio values for potential energy surface and the dipole moment compo- nents were used to construct Fortran interpolation/extrapolation subroutines that calculate the energies and dipole moments for any arbitrary geometry. The subroutines interpolate the surfaces using B splines inside the box of ab initio geometries and extrapolate the surfaces outside of the box using analytical formulas based on the theoretical asymptotic behavior. The subroutines are available from the journal’s EPAPS service. The energy surface can be used for all isotopologues of H − 3 , the dipole moment surfaces in the present form can only be used for H − 3 and D − 3 isotopologues. For the H$_{2}$D − and D$_{2}$H − molecules, the dipole moments should be transformed to account for the different orientation of axes of inertia. Using the new potential surfaces, we have calculated the bound states for the H − 3 and D − 3 isotopologues. A relatively large magnitude | D | ∼ 4 a.u. of the dipole moment near equilibrium positions for bound vibrational states and a large size of the electronic clouds of H − suggest that the cross-section for the formation of H − 3 stable molecules by the radiative association between H$_{2}$ and H − is significant. A relatively large dipole moment and existence of several bound levels suggests also that the H − 3 can be detected using the IR photoabsorption spectroscopy. The calculated energies of H − 3 bound states can also be used to search for H − 3 in the cold interstellar medium with a large fraction of ionized hydrogen (to have enough free electrons). We have developed a model for the formation of H − 3 in radiative association collisions between H$_{2}$ and H − . In the model, H − is formed by dissociative attachment of the electron to H$_{2}$. If a photoabsorption signal from H − 3 (in mm range) is detected, this would also be a signal for the presence of H − in the ISM: H − itself cannot be detected directly. 22