Production Pathways of CCS and CCCS Inferred from Their13C Isotopic Species

The rotational spectral lines (JN = 32-21 and JN = 21-10) of 13CCS and C13CS have been observed toward a cold dark cloud, TMC-1. The strongest hyperfine component lines of 13CCS and C13CS (JN = 21-10, 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, 13CCS is found to be significantly diluted. Such a difference between the 13CCS and C13CS 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 13CCCS and CCC34S 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 13CCCS is diluted as in the case of 13CCS. These results give us strong constraints on the main pathways to produce CCS and CCCS.