DETECTION OF MGCN IN IRC- A NEW METAL-BEARING FREE-RADICAL(10216 )

A new metal-containing molecule, MgCN, has been detected toward the la te-type star IRC +10216, using the NRAO 12 m and IRAM 30 m telescopes. The N = 11 --> 10, 10 --> 9, and 9 --> 8 transitions of this species, which has a (2) Sigma(+) ground state, have been observed in the oute r envelope of this object at 3 mm. For the N = 11 --> 10 transitions, the two spin-rotation components are clearly resolved and conclusively identify this new radical. These measurements imply a column density for MgCN of N-tot similar to 10(12) cm(-2) in the outer shell, which c orresponds to a fractional abundance of f similar to 7 x 10(-10). This molecule, the metastable isomer of MgNC, is the third metal-bearing s pecies thus far identified in the outer shell of IRC +10216, and its d etection implies a ratio of MgNC/MgCN similar to 22/1. MgCN may be for med through a reaction scheme involving magnesium and HNC or CN, both prominent outer shell molecules, or through synthesis on grains.