the ROSINA mass spectrometer in comet 67P provided a ratio $^{14}$N/$^{15}$N=118$\pm$25 for NH$_3$ and 130$\pm$30 for N$_2$ molecules [@Altwegg2019].

We used the $^{12}$C$^{14}$N B-X (0,0) band to estimate the $^{12}$C/$^{13}$C and $^{14}$N/$^{15}$N isotopic ratios of 21P. We used a CN fluorescence model to create synthetic spectra of $^{13}$C$^{14}$N, $^{12}$C$^{15}$N, and $^{12}$C$^{14}$N. More details of the model are given in [@Manfroid2009]. Figure \[21p\_CN\] shows the observed CN spectrum compared to the synthetic one made under the same observational conditions. The ratios found for $^{12}$C/$^{13}$C and $^{14}$N/$^{15}$N are 100$\pm$10 and 145$\pm$10, respectively. These values are consistent with those of about 20 comets with different dynamical origins, 91.0$\pm$3.6 and 147.8$\pm$5.7 for $^{12}$C/$^{13}$C and $^{14}$N/$^{15}$N respectively [@Manfroid2009; @Morvan2015].

NH$_2$ and NH$_3$ ortho-para ratios
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We measured the ortho-to-para abundance ratio (OPR) of NH$_{2}$ from the three rovibronic emissions bands (0,7,0), (0,8,0) and (0,9,0), see Figure \[fig:opr\_nh2\], following the method described in [@Shinnaka2011]. The derived OPRs of NH$_{2}$ and of its parent molecule NH$_{3}$, are listed for each band in Table \[tab\_opr\] and have average values of 3.38 $\pm$ 0.06 and 1.19 $\pm$ 0.03, respectively. The latter is in very good agreement with the Subaru/HDS determination (NH$_3$ OPR = 1.16 $\pm$ 0.02; [@Shinnaka2020]). A nuclear 