Parent molecules coming off the nucleus are decaying by photo dissociation to produce the observed daughter molecules. The model adjustment was performed at a physical distance of $10\,000$ km from the nucleus. Table \[tab:parameters\] shows the scale lengths and g-factors of different molecules at 1 au scaled by r$_h^{-2}$. More details about the Haser model and its parameters are given in our previous works (see [@Moulane2018] and references therein). We would like to point out that we used the same parameters as those from [@Schleicher2018] for the previous apparitions of 21P. We derived the Af$\rho$ parameter, a proxy for the dust production [@A'Hearn1984], from the dust profiles in the cometary dust continuum BC, GC, and RC filters and the broad-band Rc and Ic filters. It was computed at $10\,000$ km from the nucleus and corrected for the phase angle effect according to the phase function normalized at $\theta$=0$^\circ$ derived by D. Schleicher[^3].

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  Molecules                          Parent              Daughter               g-factors
                                      (km)                 (km)          erg s$^{-1}$ mol$^{-1}$
  OH(0,0)                      2.4 $\times$10$^4$   1.6 $\times$10$^5$   1.49$\times$10$^{-15}$
  NH(0,0)                      5.0 $\times$10$^4$   1.5 $\times$10$^5$   6.27$\times$10$^{-14}$
  CN($\Delta\upsilon$=0)       1.3 $\times$10$^4$   2.1 $\times$10$^5$   2.62$\times$10$^{-13}$
  C$_3$($\lambda$=4050 Å)      2.8 $\times$10$^3$   2.7 $\times$10$^5$   1.00$\times$10$^{-12}$
  C$_2$($\Delta\upsilon$=0)    2.2 $\times$10$^4$   6.6 $\times$10$^4$   4.50$\times$10$^{-13}$
  \[tab:parameters\]                                                    
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