Observed lines of the 2₀₂ − 1₀₁ transition of HCCO in TMC-1. The abscissa corresponds to the rest frequency of the lines. The v_LSR, linewidth, and integrated intensity of each line are given in Table A.1. The ordinate is the antenna temperature, corrected for atmospheric and telescope losses, in milli Kelvin. The noise of this spectrum is 0.22 mK. The quantum numbers for each transition are indicated. The hyperfine components of the fine structure transitions J = 5/2-3/2 and J = 3/2-1/2 are indicated in violet and blue, respectively. The red line shows the computed synthetic spectrum for this species (see Appendix B.2). Blank channels correspond to negative features produced in the folding of the frequency switching data.