Interstellar HCO: Detection of the Missing 3 Millimeter Quartet

All four of the strongest 1(01)-0(00) hyperfine lines of the formyl radical, HCO, have been detected for the first time in any interstellar source. Comparisons between these hyperfine lines and the J = 1-0 transition of H13CO+, which was also within the band, suggest that the column densities of HCO in the two typical molecular clouds which were sampled, DR 21 and NGC 2024, are comparable to those of H113CO+ and in excellent agreement with current theoretical chemical models for such sources. Thus, these preliminary results suggest that HCO is not underabundant in typical interstellar molecular clouds. Also, they have significant implications for the use of low sensitivity surveys to detect and analyze species with complex spectra.