Coaddition of ¹⁴ND lines. Top panel: ¹⁴ND lines selected for coaddition are indicated by vertical, dotted, purple lines listed in Table 6. The modeled ¹⁴ND spectrum in green has been intensified to have a flux similar to the observed spectrum of 73P in blue. Notice that some of the most intense lines of the ¹⁴ND modeled spectrum have not been selected for the coaddition, as they were blended with ¹⁴NH lines. Bottom panel: result of the coaddition of the ¹⁴ND lines of the observed spectrum of 73P in blue and the modeled ¹⁴ND lines in green.