Abundance ratios of N(HCO⁺)/N(CO), N(HCN)/N(CO), N(C₂H)/N(CO) and N(c-C₃H₂)/N(CO) (from left to right) predicted by the Paris-Durham shock code as a function of time with a preshock density of n_H = 2 × 10³ cm⁻³. The upper row shows the results of a nonirradiated shock, and the lower row shows the results of a shock irradiated by an interstellar radiation field (G₀ = 1.6) with a visual extinction of A_V = 2. The lines with different colors show the results of different shock velocities, as shown in the labels of the upper right panel. The gray shaded regions delineate the range obtained from our observation.