2008ApJ...673L..71S

The millimeter-wave rotational emission line (J=9-8) of the negative ion, C₄H^–, 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 C₄H^– is determined to be 1.1x10¹⁰/cm2. The [C₄H^–]/[C₄H] ratio is found to be 6.8x10^–5, which is much lower than the [C₆H^–]/[C₆H] ratio (0.093). From this result, the rate coefficient for the radiative attachment reaction between C₄ H and electron is estimated to be as small as 3x10^–11 cm3/s 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.