2021A&A...652L..13P

After the previous discovery of MgC₃N and MgC₄H in IRC +10216, a deeper Q-band (31.0-50.3 GHz) integration on this source had revealed two additional series of harmonically related doublets that we assigned on the basis of quantum mechanical calculations to the larger radicals MgC₅N and MgC₆H. The results presented here extend and confirm previous results on magnesium-bearing molecules in IRC +10216. We derived column densities of (4.7±1.3)x10¹² for MgC₅N and (2.0±0.9)x10¹³ for MgC₆H, which imply that MgC₅N/MgC₃N=0.5 and MgC₆H/MgC₄H=0.9. Therefore, MgC₅N and MgC₆H are present with column densities not so different from those of the immediately shorter analogs. The synthesis of these large magnesium cyanides and acetylides in IRC +10216 can be explained for their shorter counterparts by a two-step process initiated by the radiative association of Mg⁺ with large cyanopolyynes and polyynes, which are still quite abundant in this source, followed by the dissociative recombination of the ionic complexes.