Formation of the simplest stable negative molecular ion H3- in interstellar medium

We present the theory of radiative association of atoms and molecules, and we apply it to the (H${}_2$-H${}^{-}$) van der Waals complex. We discuss the possibility for the H${}_3^{-}$ ion to be formed in the interstellar medium in an environment with abundant ionized molecular hydrogen H${}_2^{+}$. The observation of H${}_3^{-}$ would also be a probe for the presence of H${}^{-}$ in the interstellar medium. By computing the electronic structure of the H${}_3^{-}$ ion, we determine its dipole moment, bound states, rotational constants, predissociated vibrational resonances and their lifetimes, and suggest a way to detect the ion in the interstellar medium.