Visual extinction, A_v (blue), and the calculated indene fraction in the ice with respect to H₂O (red), as a function of the position in the cloud. The dashed line on the right represents the visual extinction limit above which we expect the presence of ice (A_v,ice ≈ 1.5), and that on the left denotes the limit above which the radiation field is dominated by the secondary UV one (A_v,shield ≈ 5.4).