Time evolution of CN (red line), HCN (blue line), and CS (black line) abundances obtained with the Nahoon astrochemical code with initial parameters of n_H = 10⁴ cm⁻³, T = 10 K, and A_V = 5 mag. The initial abundances of CN, HCN, and CS equal zero at t = 0. The assumed cosmic-ray ionization rate is 1.3 × 10¹⁷ s⁻¹, dust-to-gas mass ratio is 0.01, dust grain radius is 10⁻⁵ cm, and grain density is 3 g cm⁻³.