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Abstract We present the spectroscopic characterization of cyclopropenethione in the laboratory and detect it in space using the Green Bank Telescope Observations of TMC-1: Hunting Aromatic Molecules survey. The detection of this molecule—the missing link in understanding the C₃H₂S isomeric family in TMC-1—completes the detection of all three low-energy isomers of C₃H₂S, as both CH₂CCS and HCCCHS have been previously detected in this source. The total column density of this molecule (N_Tof $5.72_{-1.61}^{+2.65}\times 10^{10}$cm⁻²at an excitation temperature of $4.7_{-1.1}^{+1.3}$K) is smaller than both CH₂CCS and HCCCHS and follows nicely the relative dipole principle (RDP), a kinetic rule of thumb for predicting isomer abundances that suggests that, all other chemistry among a family of isomers being the same, the member with the smallest dipole (μ) should be the most abundant. The RDP now holds for the astronomical abundance ratios of both the S-bearing and O-bearing counterparts observed in TMC-1; however, CH₂CCO continues to elude detection in any astronomical source. 

Abstract We present the synthesis and laboratory rotational spectroscopy of the seven-ring polycyclic aromatic hydrocarbon (PAH) cyanocoronene (C₂₄H₁₁CN) using a laser-ablation-assisted cavity-enhanced Fourier transform microwave spectrometer. A total of 71 transitions were measured and assigned between 6.8 and 10.6 GHz. Using these assignments, we searched for emission from cyanocoronene in the Green Bank Telescope (GBT) Observations of TMC-1: Hunting Aromatic Molecules project observations of the cold dark molecular cloud TMC-1 using the 100 m GBT. We detect a number of individually resolved transitions in ultrasensitiveX-band observations and perform a Markov Chain Monte Carlo analysis to derive best-fit parameters, including a total column density of $N\left({\mathrm{C}}_{24}{\mathrm{H}}_{11}\mathrm{CN}\right)=2.69_{-0.23}^{+0.26}\times 10^{12}{\mathrm{cm}}^{-2}$at a temperature of $6.05_{-0.37}^{+0.38}$K. A spectral stacking and matched filtering analysis provides a robust 17.3σsignificance to the overall detection. The derived column density is comparable to that of cyano-substituted naphthalene, acenaphthylene, and pyrene, defying the trend of decreasing abundance with increasing molecular size and complexity found for carbon chains. We discuss the implications of the detection for our understanding of interstellar PAH chemistry and highlight major open questions and next steps.