Fractional ice abundances of main species formed from O, O₂, and CO for three reference models with “normal” gas phase abundances computed with the chemical network presented in Sect. 2.2 (left), and for a gas phase [O₂]/[O] abundance ratio artificially decreased by a factor of 10 (right): top n_H = 1 × 10⁴ cm^-3, T = 15 K, A_V = 2 mag, middle n_H = 1 × 10⁴ cm^-3, T = 10 K, A_V = 4 mag, bottom n_H = 1 × 10⁵ cm^-3, T = 10 K, A_V = 10 mag. Values of other parameters are bold values of Table 5.