The most promising optical cycling scheme is the that of the NbN + cation. The calculated FCFs show that with lasers addressing the ν ′′ = 0 → ν ′ = 0 and ν ′′ = 1 → ν ′ = 0 branches this molecule should be able to scatter on average more than 10 5 photons before population leaks to ν ′′ > 1 states. This number of scattering events should be sufficient for laser cooling, however, direct laser cooling on a transition with a radiative lifetime of the order of hundreds microseconds is not attractive.