Comparison of the fractional abundances, n(x)/n_H, for Model 1 (G₀ = 10⁴ and n_H = 10⁴ cm^-3), considering bare grains f_ice = 0 (solid line) and icy grains f_bare = 0 (dashed line). Left panel: H, CO, O₂, H₂O, H₂CO, and CH₃OH. Right panel: solid CO, CO₂, H₂O, H₂O₂, and CH₃OH. The dash-dotted black line represents the number of possible attachable sites on grain surfaces per cm³ (the limit to form one full monolayer of ice).