Presentation #135.04 in the session Molecular Cloud Chemistry.
In a previous study, methanol, CH3OH, was observed towards 20 molecular clouds located in the outer Galaxy (RGC = 12.9-23.5). The abundance of CH3OH did not appear to decrease significantly with distance from the Galactic Center and apparently is not affected by the decline in metallicity. These detections suggest an “Organic Zone,” a region of the Galaxy where organic chemistry is active. In order to further define the Organic Zone, we have been searching for c-C3H2, NO, and CH3CN in the “edge” molecular clouds where CH3OH has been detected. Part of these observations are being conducted with a new 2 mm receiver at the 12m telescope of the Arizona Radio Observatory (ARO). Detections of the J=4→3 transitions of c-C3H2, as well as hyperfine components of the J=3/2→1/2 transition of NO, have been made in almost all 20 clouds of the sample, including WB89-640, WB89-380, and 19423+2541. Multiple K components of the J =5→4 transition of CH3CN have also been identified in WB89-640. From a radiative transfer analysis, fractional abundances of the three molecules, relative to H2, are f ~ 10-11, f ~ 10-10, and f ~10-9 for CH3CN, c-C3H2, and NO, respectively. Preliminary results suggest that abundances of these species are comparable to those in the inner Galaxy. The detection of c-C3H2, NO, and CH3CN at the Galactic edge suggest that organic chemistry is still active despite the decrease in metallicity. Additional observations of CH3CN are currently being conducted.