The problem of X-ogen.

Four new galactic sources exhibiting emission from the unidentified line X-ogen are reported. A rest frequency of 89.189 GHz is derived from the new sources. Several possible molecules with calculated transition frequencies near the X-ogen line are considered; however, identifications of HNC, HCO +, or CCH with X-ogen are difficult until more spectroscopic evidence is available. The molecular-hydrogen density necessary to excite the various molecules seen in Orion is derived and related to the angular size of the region observed. The results suggest a cloud elongated in the N-S direction and centered on the OH and H2O maser position with densities of H2 increasing from 10 cm-3 at the edge to 108 at the center. Subject headings: line identifications - molecules, interstellar - Orion Nebula - radio lines