Effects of CR induced desorption (CRID). Time evolution of the abundances of the Case 1 species CO (left), HCO⁺ (middle) and N₂H⁺ (right) in the models with n_H = 1.0 × 10⁵ cm⁻³, T = 15 K and A_v = 20 mag for several different CRIRs. The dotted lines show the fiducial case in which CRID is not included. The dashed lines show the case in which CRID is included with a standard rate (see text). The horizontal bands show the observed abundances together with their uncertainties at P2.