  This paper deals with the possible formation of two molecular anions often
considered likely components in the physical environments of the Interstellar
Medium ( ISM) : $\mathrm{C_2H^-}$ and $\mathrm{NCO^-}$. They are both discussed
here by computationally following the radiative association (RA) mechanism
starting from $\mathrm{C_2^-}$, $\mathrm{H}$, $\mathrm{NC^-}$ and $\mathrm{O}$
as partners. The corresponding RA total cross sections produced by the
calculations are in turn employed to generate the overall association rates
over the relevant range of temperatures. The latter are found to be in line
with other molecular ions formed by RA but not large enough to uniquivocally
suggest this path as the main route to the anions formation in the ISM. Other
possible paths of formation are also analysed and discussed. The presence of
resonant structures during the association dynamics for both systems is found
by the calculations and their consequences are discussed in some detail in the
present study.
