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C. Savage, A.J. Apponi, L.M. Ziurys (Steward Observatory, The University of Arizona)
The N = 1 arrow 0, J = 3/2 arrow 1/2 transitions of 12CN and 13CN (X2\Sigma+) at 113.5 and 108.8 GHz, respectively, were observed in a sample of 10 galactic molecular clouds using the Kitt Peak 12-meter telescope. The objects studied were W3(OH), W49, DR-21(OH), G34.3, Orion-KL, W51M, NGC 7538, NGC 2024, L134N, and TMC-1. Hyperfine structure was resolved in the spectra of both molecules, enabling an accurate determination of optical depth for 12CN and 13CN. From these measurements, calculations of 12C/13C ratios were carried out for all these sources. Typical values found are 12C/13C ~ 30-60, with the exception of NGC 2024, where the ratio was near 100. The carbon isotope ratios found with these observations thus tend to be lower than those derived from other molecules, such as H2CO. However, there still appears to be an increase in the 12C/13C ratio with distance from the galactic center.