Laboratory and astronomical discovery of magnesium dicarbide, MgC${}_2$

Abstract

We report the detection of magnesium dicarbide, MgC${}_2$, in the laboratory at centimeter wavelengths and assign ${}^{24}$MgC${}_2$, ${}^{25}$MgC${}_2$, and ${}^{26}$MgC${}_2$ to 14 unidentified lines in the radio spectrum of the circumstellar envelope of the evolved carbon star IRC+10216. The structure of MgC${}_2$ is found to be T-shaped with a highly ionic bond between the metal atom and the C${}_2$ unit, analogous to other dicarbides containing electropositive elements. A two-temperature excitation model of the MgC${}_2$ emission lines observed in IRC+10216 yields a very low rotational temperature of $6\pm 1$ K, a kinetic temperature of $22\pm 13$ K, and a column density of $(1.0\pm 0.3)\times 10^{12}$ cm${}^{-2}$. The abundance of MgC${}_2$ relative to the magnesium-carbon chains MgCCH, MgC${}_4$H, and MgC${}_6$H is $1:2:22:20$ and provides a new constraint on the sequential radiative association-dissociative recombination mechanisms implicated in the production of metal-bearing molecules in circumstellar environments.

15 pages, 5 figures

References in corpus (2)

• Magnesium radicals MgC${}_5$N and MgC${}_6$H in IRC+10216
• A 1.3 cm line survey toward IRC +10216

Cited by in corpus (5)

• The magnesium paradigm in IRC+10216: Discovery of MgC${}_4$H${}^{+}$, MgC${}_3$N${}^{+}$, MgC${}_6$H${}^{+}$, and MgC${}_5$N${}^{+}$
• Discovery of two metallic cyanoacetylides in IRC+10216: HMgCCCN and NaCCCN
• Detection of the linear SiC${}_3$ and SiC${}_5$ radicals in IRC\,+10216
• Leveraging MMW-MMW Double Resonance Spectroscopy to Understand the Pure Rotational Spectrum of Glycidaldehyde and 17 of Its Vibrationally Excited States
• Development of a glow-discharge ion-trap instrument for measuring effective radiative-association rate coefficients