Letter to the Editor

Discovery of two new magnesium-bearing species in IRC+10216: MgC₃N and MgC₄H^⋆

¹ Grupo de Astrofísica Molecular. Instituto de Física Fundamental (IFF-CSIC), C/Serrano 121, 28006 Madrid, Spain
e-mail: jose.cernicharo@csic.es
² Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
³ Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain
⁴ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d’Hères, France
⁵ Department of Applied Chemistry, Science Building II, National Chiao Tung University, 1001 Ta-Hsueh Rd., Hsinchu 30010, Taiwan

Received: 24 July 2019
Accepted: 20 August 2019

Abstract

We report on the detection of two series of harmonically related doublets in IRC +10216. From the observed frequencies, the rotational constant of the first series is B = 1380.888 MHz and that of the second series is B = 1381.512 MHz. The two series correspond to two species with a ²Σ electronic ground state. After considering all possible candidates, and based on quantum chemical calculations, the first series is assigned to MgC₃N and the second to MgC₄H. For the latter species, optical spectroscopy measurements support its identification. Unlike diatomic metal-containing molecules, the line profiles of the two new molecules indicate that they are formed in the outer layers of the envelope, as occurs for MgNC and other polyatomic metal-cyanides. We also confirm the detection of MgCCH that was previously reported from the observation of two doublets. The relative abundance of MgC₃N with respect to MgNC is close to one while that of MgC₄H relative to MgCCH is about ten. The synthesis of these magnesium cyanides and acetylides in IRC +10216 can be explained in terms of a two-step process initiated by the radiative association of Mg⁺ with large cyanopolyynes and polyynes followed by the dissociative recombination of the ionic complexes.