articleAstronomy and AstrophysicsJan 20, 2026DIAMOND OA

Discovery of 1 H -cyclopent[ cd ]indene ( c -C 11 H 8 ) in TMC-1 with the QUIJOTE line survey: A new three-ringed polycyclic aromatic hydrocarbon

Instituto de Física Fundamental · Yebes Observatory · +1 more institution

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Abstract

We report the detection of the polycyclic aromatic hydrocarbon (PAH) 1 H -cyclopent[ cd ]indene ( c -C 11 H 8 ) in TMC-1 with the QUIJOTE line survey. We detected 22 independent lines corresponding to 88 rotational transitions with quantum numbers ranging from J = 19 up to J = 24 and K a ≤ 5 in the Q -band range. The identification of this new PAH was based on the agreement between the rotational parameters derived from the analysis of the lines and those obtained by quantum chemical calculations. The column density derived for 1 H -cyclopent[ cd ]indene is (6.0 ± 0.5) × 10 12 cm −2 , with a rotational temperature of 9 K. Its abundance is high, as is that of the rest of the PAHs, but it is the lowest of all…

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Topics & keywords

Keywords
  • Indene
  • Polycyclic aromatic hydrocarbon
  • Line (geometry)
  • Hydrocarbon
  • Spectral line
  • Quantum
  • Quantum chemical
  • Abundance (ecology)
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