Tentative Detection of C 4 H - toward the Low-Mass Protostar IRAS 04368+2557 in L1527

The millimeter-wave rotational emission line ( J = 9–8) of the negative ion, C 4 H − , has tentatively been detected toward the low-mass Class 0 protostar IRAS 04368+2557 in L1527 with the IRAM 30 m telescope. The column density of C 4 H − is determined to be 1.1 × 10 10 cm −2 . The [C 4 H − ]/[C 4 H] ratio is found to be 6.8 × 10 −5 , which is much lower than the [C 6 H − ]/[C 6 H] ratio (0.093). From this result, the rate coefficient for the radiative attachment reaction between C 4 H and electron is estimated to be as small as 3 × 10 −11 cm 3 s −1 on the basis of the simplified chemical model. The present observation has demonstrated the uniqueness and importance of L1527 in searching for a new carbon-chain molecule in a star-forming region.