Modified Loomis–Wood diagram of some of the observed lines of cyclopentindene. The abscissa corresponds to the value of the rotational constant, which has been fixed in this plot to values between 819.6 and 820.6 MHz. The ordinate is the antenna temperature, corrected for atmospheric and telescope losses, in millikelvin. The frequency represented in each box corresponds to 2 B_rotJ, where J = J_u + 1/2. The red lines represent a synthetic spectrum of the lines detected with the QUIJOTE data. The blue solid lines correspond to the new detected lines in this work, while dotted lines correspond to transitions with the same K_a (for all transitions involved, see Table B.1).