Molecular abundances relative to H₂ predicted by models A to D. The input parameters of these models are shown in Table 4. The red line represents the [HCN]/[H₂] ratio, the purple line shows the [HCO⁺]/[H₂] ratio, and the blue line shows the [C₂H]/[H₂] ratio. The dashed lines shows the ratios of observational results toward MonR2 for the 10.5 km s^-1 component at the IF position.