2₀₂ ← 1₁₁ to 1₁₁ ← 0₀₀ opacity ratios of cyclic para-cyclopropenylidene (para c-C₃H₂) under optically thin conditions as a function of density and temperature. Depending on the continnum source-covering factors used (see subsection c-C₃H₂ in Sect. 4.2), we obtain ratios of 0.87 ± 0.19 and 1.14 ± 0.25. Both values are below the modeled ones, but accounting for the errors, they are not inconsistent with the standard values of T_kin = 50−80 K and n(H₂) = 1000−2000 cm^-3 (Henkel et al. 2008; 2009; Muller et al. 2011; 2013).