Ro-vibrational diagrams of absorption components of the infrared HCN lines at 7.5 and 13–14 μm. The filled blue, magenta, brown, and red dots correspond to the lines of the bands 2ν₂ (σ⁺), 3ν₂ (π) − ν₂(π), 4ν₂ (σ⁺) − 2ν₂(σ⁺), and 4ν₂ (δ) − 2ν₂(δ), respectively (7.5 μm). The empty blue, magenta, and brown empty triangles represent the lines of the bands ν₂ (π), 2ν₂ (σ⁺) − ν₂(π), and 2ν₂ (δ) − ν₂(π) at 13–14 μm. The dots related to the hot bands (except 4ν₂(σ⁺) − 2ν₂(σ⁺) and 4ν₂ (δ) − 2ν₂(δ); see text) are vertically shifted to make them coincide with the fundamental band at 13–14 μm and with thefirst overtone at 7.5 μm to get more populated data sets. An additional offset of − 2 units is added to the data at 13–14 μm to improve visibility. Four populations with various rotational temperatures derived from the fitted solid straight lines can be distinguish (cold, warm, hot, and very hot). The dashed straight line is a fit to the lines of the 4ν₂ (σ⁺) − 2ν₂(σ⁺) band, which implies a negative rotational temperature (see text). is defined as N_col,0Z_rote^y₀ (Eq. (2)).