Time evolution of the HCN/HC¹⁵N ratio in simulations S1 to S3, labeled in the top panel (data reproduced from Fig. 2). The top panel displays the ratio as predicted directly in the simulations, while in the bottom panel, the HCN abundance has been derived by scaling the simulated H¹³CN abundance by a factor of 68. The logarithmic scaling of the y-axis in both panels was employed here to accentuate the magnitude of the differences between the results. The dashed black line in each panel indicates the assumed elemental ¹⁴N/¹⁵N ratio (440).