Formation of negative molecular ions $M$H$^-$ in the interstellar medium by radiative association of a molecule $M$ and an H$^-$ ion

We consider if negative molecular ions of the type $M$H$^-$ can be formed in the interstellar medium by radiative association of the negative hydrogen ion H$^-$ (RAH$^-$) to a molecule $M$. For this goal, we consider the CO and H$_2$O molecules, which are abundant in the ISM, as candidates for $M$. We have determined {\it ab initio} potential energy surfaces and dipole moments for COH$^-$ and H$_3$O$^-$ ions. The two molecular ions are bound. We will present a preliminary estimation of the rate coefficients of RAH$^-$ to H$_2$O and CO. We have also determined rotational constants of COH$^-$ and H$_3$O$^-$ ions that allows us to construct theoretical IR spectra for these ions. Previously, we have found that IR absorption frequencies for H$_3^-$ are out of range of the orbital telescopes, but the IR absorption spectra for COH$^-$, and H$_3$O$^-$ are within the range of wavelengths of Herschel telescope, which could be used to detect such ions. An eventual observation of $M$H$^-$ would indicate that the H$^-$ ion is also present in the interstellar medium.