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We report the identiÐcation of 10 transitions that support the detection of the small cyclic molecule ethylene oxide (cin Sgr B2N. Although one of these transitions is severely blended, so that an C 2 H 4 O) accurate intensity and line width could not be determined, and two other lines are only marginally detected, we have done Gaussian Ðts to the remaining seven lines and have performed a rotation diagram analysis. Our results indicate a rotation temperature K and a molecular column T rot \ 18 density N(ccm~2, corresponding to a fractional abundance relative to molecular C 2 H 4 O) \ 3.3 ] 1014 hydrogen of order 6 ] 10~11. This is a factor of more than 200 higher than the abundance for this molecule suggested by the "" new standard ÏÏ chemistry model of Lee, Bettens, & Herbst. This result suggests that grain chemistry might play an e †ective role in the production of No transitions of this c-C 2 H 4 O. molecule were detected in either Sgr B2M or Sgr B2NW.

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The rotational spectral lines (J N ¼ 3 2 Y2 1 and J N ¼ 2 1 Y1 0 ) of 13 CCS and C 13 CS have been observed toward a cold dark cloud, TMC-1. The strongest hyperfine component lines of 13 CCS and C 13 CS (J N ¼ 2 1 Y1 0 , F ¼ 5/2Y3/2) have successfully been detected. The C 13 CS ½ / 13 CCS ½ abundance ratio is determined to be 4:2 AE 2:3 (3 ). The CCS ½ / 13 CCS ½ ratio is evaluated to be 230 AE 130 (3 ), and hence, 13 CCS is found to be significantly diluted. Such a difference between the 13 CCS and C 13 CS abundances is also found in L1521E, which is a very young core with rich carbon-chain molecules. Therefore, the anomaly is not specific to TMC-1, but seems to be common for the CCS-rich clouds. Furthermore, we have also observed the J ¼ 4Y3 transition of 13 CCCS and CCC 34 S in TMC-1 and L1521E and have found that the CCC 34 S ½ / 13 CCCS ½ ratio is larger than 8.4 (3 ). This lower limit is considerably larger than the interstellar 12 C ½ 34 S ½ / 13 C ½ 32 S ½ ratio of 3, indicating that 13 CCCS is diluted as in the case of 13 CCS. These results give us strong constraints on the main pathways to produce CCS and CCCS.