HDO / H₂O ratio in the bulk ice in the two grids (with and without the reaction-diffusion competition) of models as functions of A_V. For the case without the competition (yellow), the solid line represents the model with N_act = 4, E_des(H₂) = 550 K, and the low-metal abundances. The areas represent the models including variations in N_act and E_des(H₂), while the light-colored areas represent the models including variations in N_act, E_des(H₂), and the initial abundances. For the case with the competition, the models with different E_des(H₂) are shown by different colors. The solid lines represent the models with N_act = 4. The areas represent models including the variations in N_act, while the light-colored areas represent the models including the variations in N_act and the initial abundances. The vertical dashed and dotted lines indicate the regions where the fraction of elemental oxygen in the atomic form becomes less than 10% and 1%, respectively, in the models represented by the solid lines.