We present a new theoretical method to treat the atom-diatom radiative association within a time independent approach. This method is an adaptation of the driven equations method developed for photodissociation. The bound state energies and wave functions of the molecule are calculated exactly and used to propagate the overlap with the initial scattering wave function. In the second part of this paper, this approach is applied to the radiative association of the N2H- anion. The main features of the radiative association cross sections are analysed and the magnitude of the calculated rate coefficient at 10 K is used to discuss the existence of the N2H - in the interstellar medium which could be used as a tracer of both N2 and H-.