Reaction pathways to form HCN and C₂H₂ in the close mid-plane, where n_〈H〉> = 2 × 10¹¹ cm⁻³, T_g = 640 K, T_d = 630 K, A_V,rad = 7, and A_V = 0.7. The major species are marked with thick boxes. Red species are rare and created by X-ray processes. The green numbers are the particle concentrations n_mol/n_〈H〉, and the blue numbers are the rates [cm⁻³s⁻¹]. Wiggly arrows indicate photodissociation, and red arrows indicate X-ray processes: XPHOT is the X-ray primary ionisation of He, and XG and XI are the X-ray secondary ionisations by fast electrons.