Authors: Changala, P. B.; Gupta, H.; Cernicharo, J.; Pardo, J. R.; Agundez, M.; Cabezas, C.; Tercero, B.; Guelin, M.; McCarthy, M. C.
Journal: ASTROPHYSICAL JOURNAL LETTERS
Publication date: 2022/12/01
Abstract: We report the detection of magnesium dicarbide, MgC2, in the laboratory at centimeter wavelengths and assign (MgC2)-Mg-24, (MgC2)-Mg-25, and (MgC2)-Mg-26 to 14 unidentified lines in the radio spectrum of the circumstellar envelope of the evolved carbon star IRC+10216. The structure of MgC2 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 MgC2 emission lines observed in IRC+10216 yields a very low rotational temperature of 6 +/- 1 K, a kinetic temperature of 22 +/- 13 K, and a column density of (1.0 +/- 0.3) x 10(12) cm(-2). The abundance of MgC2 relative to the magnesium-carbon chains MgCCH, MgC4H, and MgC6H 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.
