Zoom-in of the Spitzer spectra for targets with CO₂ ice absorption. Absorption optical depths τ near 15 μm were derived from F = F₀e^−τ, where F is the observed flux density, and F₀ is the continuum derived from a continuum fit, obtained with a polynomial of degree N = 3 (red curve; HH 381 IRS, V883 Ori, BRAN 76, and V733 Cep needed N = 2) to fit the ranges 13.5–14.7 and 18.2–19.5 μm (except for HH 381 IRS and V883 Ori for which 13.5–14.7 and 16.0–17.0 μm were used). In addition, in some cases, a Gaussian function centered on 608 cm⁻¹ (16.45 μm) and of FWHM = 73 cm⁻¹ was added tofit the 16.5-18.2 μm range to account for absorption due to silicates. This method is similar to that used by Pontoppidan et al. (2008). Interestingly, we detect gas absorption by CO₂ at 15.0 μm, but only in PP13 S.