Observed transitions of H₂CCCHCCH towards TMC-1. The abscissa corresponds to the rest frequency of the lines assuming a local standard of rest velocity of the source of 5.83 km s⁻¹. Frequencies and intensities for the observed lines are given in Table A.1. The ordinate is the antenna temperature, corrected for atmospheric and telescope losses, in millikelvin. The violet line shows the computed synthetic spectrum for this species for T_r = 7 K and a column density of 1.2 × 10¹³ cm⁻². Cyan stars indicate the position of negative features produced in the folding of the frequency switching observations.