Comparison of our modeling of ¹²CO⁺ spectrum with our observational data obtained on comet C/2016 R2 for the three different settings. The observational spectra appear in blue, while the model is in red (for clarity it appears with a negative scale). The different CO⁺ bands bright enough to be detected in the observational spectrum are identified in red for the model. The (6,0), (7,1), and (6,1) CO⁺ bands appear (weakly) on the observational spectrum and are identified in blue, but not on the model because this one is restricted to v″ and v′ ≤ 5. The intensity scale is arbitrary but proportional to units of ergs s^-1. Some other species appear in the observational spectrum (e.g., and CN emission lines near the (5,1) CO⁺ band).