ASTRONOMICAL SEARCH AND LABORATORY SPECTROSCOPY OF THE FECO RADICAL

The millimeter and submillimeter spectrum of the FeCO radical in the ( 3) Sigma(-) ground electronic state has been observed in the laborator y. The radical was generated by a DC glow discharge in a mixture of Fe (CO)(5) and argon. A total of 33 rotational transitions in the three s pin sublevels with Omega = 1, 0 were observed in the frequency region between 223 and 372 GHz. The observed frequencies were analyzed using a Hamiltonian for the 3 Sigma(-) state, and the rotational, centrifuga l distortion, spin-spin coupling, and spin-rotation coupling constants were determined. Based on these constants, we obtained the rest frequ encies in the 2 and 3 mm regions of FeCO and searched for this radical toward the circumstellar envelope of IRC + 10216 and the star-forming regions W3(OH), DR 21, and Sgr B2 with the Institute de Radioastronom ia Milimetrica 30 m radio telescope. The FeCO lines were not detected with an rms noise of 3-7 mK in four sources. The upper limit on the Fe CO column density was estimated to be 3 x 10(13) cm(-2) in IRC + 10216 .