RADIO SEARCH FOR H sub(2)CCC TOWARD HD 183143 AS A CANDIDATE FOR A DIFFUSE INTERSTELLAR BAND CARRIER

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