Example of line identification, decomposition, and fitting of our Q-Band IRC+10216 spectrum around J_up = 58 for several HC₉N ν₁₉ vibrational states (1,2,3,4) found in this work. The top panel shows individual line contributions (several colors are used to distinguish them if necessary), middle panels show the resulting combination on top of the data, and the lower panel shows fit residuals.