Letter to the Editor

Magnesium radicals MgC₅N and MgC₆H in IRC +10216^⋆

¹ Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas, C/ Serrano 123, 28006 Madrid, Spain
e-mail: jr.pardo@csic.es, jose.cernicharo@csic.es
² Instituto Geográfico Nacional, Centro de Desarrollos Tecnológicos, Observatorio de Yebes, Apartado 148, 19080 Yebes, Spain
³ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 St-Martin d’Hères, France

Received: 29 June 2021
Accepted: 26 July 2021

Abstract

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) × 10¹² for MgC₅N and (2.0 ± 0.9) × 10¹³ 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.