Observed lines of H₂CCC in the 31-115 GHz domain toward TMC-1. The abscissa corresponds to the velocity of the cloud with respect to the Local Standard of Rest (v_LSR). The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. The spectral resolution is 38 kHz below 50 GHz and 48 kHz above. Derived line parameters are given in Table B.2. The red lines show the computed synthetic spectra for the lines of H₂CCC (see text). The lines in the left column correspond to para lines of H₂CCC, while those of the central and right columns correspond to transitions of the ortho species. The adopted frequencies are those of the CDMS catalog (Müller et al. 2005) and are given in Table B.2.