To clarify the authenticity of a recently proposed identification of H 2 CCC (linear-C 3 H 2 ) as a diffuse interstellar band carrier, we searched for the rotational transition of H 2 CCC at a frequency of 103 GHz toward HD 183143 using a 45-m telescope at the Nobeyama Radio Observatory. Although rms noise levels of 32 mK in the antenna temperature were achieved, detection of H 2 CCC was unsuccessful, producing a 3 σ upper limit corresponding to a column density of 2.0 × 10 13 cm −2 . The upper limit indicates that the contribution of H 2 CCC to the diffuse interstellar band at 5450 Å is less than 1/25; thus, it is unlikely that the laboratory bands of the B 1 B 1 -X 1 A 1 transition of H 2 CCC and the diffuse interstellar bands at 5450 Å (and also 4881 Å) toward HD 183143 are related.

We report a sensitive search for the rotational transitions of the carbon-chain alcohol HC 4 OH in the frequency range 21.2-46.7 GHz in the star-forming region L1527 and the dark cloud TMC-1. The motivation was laboratory detection of HC 4 OH by microwave spectroscopy. Despite achieving rms noise levels of several millikelvin in the antenna temperature using the 45 m telescope at Nobeyama Radio Observatory, the detection was not successful, leading to 3σ upper limits corresponding to the column densities of 2.0 × 10 12 and 5.6 × 10 12 cm −2 in L1527 and TMC-1, respectively. These upper limits indicate that [HC 4 OH]/[HC 5 N] ratios are less than 0.3 and 0.1 in L1527 and TMC-1, respectively, where HC 5 N is an HC 4 -chain cyanide and HC 4 OH is a hydroxide. These ratios suggest that the cyano carbon-chain molecule dominates the hydroxyl carbon-chain molecule in L1527 and TMC-1. This is contrary to the case of saturated compounds in hot cores, e.g., CH 3 OH and CH 3 CN, and can be a chemical feature of carbon-chain molecules in L1527 and TMC-1. In addition, the column densities of the "unsubstituted" carbon-chain molecule C 4 H and the sulfur-bearing molecules SO and HCS + were determined from detected lines in L1527.