Discovery of 1H-cyclopent[cd]indene (c-C11H8) in TMC-1 with the QUIJOTE line survey: A new three-ringed polycyclic aromatic hydrocarbon

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Volume 706 (February 2026)

A&A, 706 (2026) L10

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Table A.1.

Experimental and theoretical molecular constants of cyclopentindene.

Parameter	1H-cyclopent[cd]indene^a	2H-cyclopent[cd]indene^a	TMC-1 (III^l)

A/MHz	1809.3791	1769.6150	1804.613(71)^b
B/MHz	1490.4924	1510.4163	1490.725(56)
C/MHz	821.38945	818.97200	820.77500(68)
Δ_J/Hz	45.05	46.95	51.0(45)
Δ_JK/Hz	-59.98	-66.53	-66.5(50)
Δ_K/Hz	19.75	24.42	[19.75]^c
δ_J/Hz	-3.72	-4.73	[-3.72]
δ_K/Hz	24.74	20.26	[24.74]

N_trans^d,N_lines^e			88, 22
J_max, K_a, max			24, 6
σ(kHz)^f,σ_w^g			6.2, 0.65
μ_a,μ_b	0.60, 0.80	0.28, 1.12

Notes.

^(a)

B3LYP/6-311++G(d,p) level of theory.

^(b)

The uncertainties (in parentheses) are in units of the last significant digits.

^(c)

Values in square brackets have been kept fixed to the theoretical values.

^(d)

Total number of rotational transitions.

^(e)

Total number of independent frequencies.

^(f)

Standard root mean square deviation of the fit in kHz.

^(g)

Weighted root mean square deviation of the fit, unitless.

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