Main mid-IR absorptions in pure ices and in binary and ternary mixtures: (a) OH stretching modes (ν₁,ν₃) of H₂O; (b) antisymmetric stretching mode (ν₃) of CO₂; (c) stretching mode (ν) of CO; (d) bending (ν₂) and libration (ν₁) modes of H₂O near 1650 and 750 cm⁻¹, respectively, and bending mode (ν₂) of CO₂ near 657 cm⁻¹ ; (e) enlargement of the ν₂ mode of CO₂. All bands of a given species presented in a panel correspond to the same number of molecules of that species. Specifically, in panels (a) and (d), N_H2O = 4.8 × 10¹⁷ molecules cm⁻²; in panels (b) and (e) N_CO2=1.7 × 10¹⁷ molecules cm⁻² ; and in panel (c) N_CO = 4.0 × 10¹⁷ molecules cm⁻².