Measured time evolutions of normalized numbers (n_x(t)/n_Σ0) of NH and NH ions in the trap filed with He/H₂ gas mixture after the injection of N⁺ ions from the SIS and fast formation of NH ions. The collisional temperature is T = 16 K, hydrogen number density is [H₂]=5.7 × 10¹⁰ cm³ s⁻¹ and helium number density is [He]=5.6 × 10¹³ cm³ s⁻¹. The fitted solution of the corresponding system of rate equations is indicated with the solid lines. The crosses (×) indicate the sum of the normalized numbers of all ions in the ion trap (Σ(t)).