Production Pathways of CCS and CCCS Inferred from Their¹³C Isotopic Species

The rotational spectral lines ( J N = 3 2 -2 1 and J N = 2 1 -1 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 = 2 1 -1 0 , F = 5/2-3/2) have successfully been detected. The / abundance ratio is determined to be 4.2 ± 2.3 (3 σ). The / ratio is evaluated to be 230 ± 130 (3 σ), 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 = 4-3 transition of 13 CCCS and CCC 34 S in TMC-1 and L1521E and have found that the / ratio is larger than 8.4 (3 σ). This lower limit is considerably larger than the interstellar / 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.