A universal method has been developed for measuring spectra of molecular ions in a 22-pole radio frequency trap at 5 K. It is based on laser induced inhibition of complex growth (LIICG). The first successful measurements have been demonstrated on the A²Π_u ← X²Σ_g⁺ electronic transition with some thousand N₂⁺ ions, helium densities of 10¹⁵ cm^–3, and storage times of 1 s. The reduction of the number of N₂⁺–He complexes is the result of an interplay between excitation, radiative and collisional cooling, ternary association, and collision induced dissociation, which is explained by a kinetic model.