Laboratory and Astronomical Detection of the (25) MgNC and (26) MgNC Radicals

Rotational spectra of the (25) Mg and (26) Mg isotopomers of MgNC have been recorded in the laboratory using mm/sub-mm direct absorption spectroscopy. Seven transitions of (26) MgNC and three transitions of (25) MgNC were measured in the frequency range 298-380 GHz. Rotational and fine structure parameters were determined for both species, as well as hyperfine constants for (25) MgNC. These measurements have resulted in the identification of (25) MgNC and (26) MgNC in the circumstellar envelope of IRC+10216, and determination of the (24) Mg:(25) Mg:(26) Mg ratio in the outer shell of this late-type star.