As in Fig. 1, but adopting additional mechanisms on the basis of fiducial model 1. In panels A–C the chain reaction mechanism for the products of Langmuir-Hinshelwood reactions, photodissociation, and adsorption is considered, respectively. In panel D the chain reaction mechanism for all three types of products is considered. In panel E a_RRK = 0.1 is used. In panel F E_b = 0.3E_d is used. In panels G–L the abscissae start with the abundances at t_total = 10⁶ yr in fiducial model 1, which correspond to t_total − 10⁶ yr. In panels G–I a case with a shock is considered, assuming peak temperatures of T_peak = 200 or 1000 K, and shock duration of t = 10² or 10⁴ yr. In panels J–L a case with an X-ray burst is considered, which is described in the models by the elevated cosmic ray ionization rate ζ_CR = 1.3 × 10⁻¹⁴ s⁻¹ or 1.3 × 10⁻¹³ s⁻¹ during a short timescale of t = 10² or 10⁴ yr, respectively.After the shock or the X-ray burst, all parameters are assumed to be the same as in fiducial model 1.