Tentative detection of C4H- toward the low-mass protostar IRAS 04368+2557 in L1527

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 1.1 x 10(10) cm(-2). The [C4H-]/[C4H] ratio is found to be 6.8 x 10(-5), which is much lower than the [C6H]/[C6H] ratio (0.093). From this result, the rate coefficient for the radiative attachment reaction between C4H and electron is estimated to be as small as cm3s 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.