Detection of the propargyl radical at lambda 3 mm

Abstract

We report the detection of the propargyl radical (CH2CCH) in the cold dark cloud TMC-1 in the lambda 3 mm wavelength band. We recently discovered this species in space toward the same source at a wavelength of lambda 8 mm. In those observations, various hyperfine components of the 2,0,2-1,0,1 rotational transition, at 37.5 GHz, were detected using the Yebes 40m telescope. Here, we used the IRAM 30m telescope to detect ten hyperfine components of the 5,0,5-4,0,4 rotational transition, lying at 93.6 GHz. The observed frequencies differ by 0.2 MHz with respect to the predictions from available laboratory data. This difference is significant for a radioastronomical search for CH2CCH in interstellar sources with narrow lines. We thus included the measured frequencies in a new spectroscopic analysis to provide accurate frequency predictions for the interstellar search for propargyl at mm wavelengths. Moreover, we recommend that future searches for CH2CCH in cold interstellar clouds are carried out at lambda 3 mm, rather than at lambda 8 mm. The 5,0,5-4,0,4 transition is about five times more intense than the 2,0,2-1,0,1 one in TMC-1, which implies that detecting the former requires about seven times less telescope time than detecting the latter. We constrain the rotational temperature of CH2CCH in TMC-1 to 9.9 +/- 1.5 K, which indicates that the rotational levels of this species are thermalized at the gas kinetic temperature. The revised value of the column density of CH2CCH (including ortho and para species) is (1.0 +/- 0.2)e14 cm-2, and thus the CH2CCH/CH3CCH abundance ratio is revised from slightly below one to nearly one. This study opens the door for future detections of CH2CCH in other cold interstellar clouds, making possible to further investigate the role of this very abundant hydrocarbon radical in the synthesis of large organic molecules such as aromatic rings.

Accepted for publication in A&A

References in corpus (13)

• Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering
• Discovery of the Pure Polycyclic Aromatic Hydrocarbon Indene ($c$-C${}_9$H${}_8$) with GOTHAM Observations of TMC-1
• Discovery of Interstellar Propylene (CH_2CHCH_3): Missing Links in Interstellar Gas-Phase Chemistry
• Discovery of benzyne, o-C6H4, in TMC-1 with the QUIJOTE line survey
• Yebes 40 m radio telescope and the broad band NANOCOSMOS receivers at 7 mm and 3 mm for line surveys
• A New Reference Chemical Composition for TMC-1
• Early Science from GOTHAM: Project Overview, Methods, and the Detection of Interstellar Propargyl Cyanide (HCCCH${}_2$CN) in TMC-1
• Discovery of two isomers of ethynyl cyclopentadiene in TMC-1: Abundances of CCH and CN derivatives of hydrocarbon cycles
• Discovery of HC4NC in TMC-1: A study of the isomers of HC3N, HC5N, and HC7N
• Discovery of the propargyl radical (CH2CCH) in TMC-1: one of the most abundant radicals ever found and a key species for cyclization to benzene in cold dark clouds
• Discovery of CH2CHCCH and detection of HCCN, HC4N, CH3CH2CN, and, tentatively, CH3CH2CCH in TMC-1
• Free Radicals in Superfluid Liquid Helium Nanodroplets: A Pyrolysis Source for the Production of Propargyl Radical
• Space and laboratory observation of the deuterated cyanomethyl radical HDCCN

Cited by in corpus (6)

• Discovery of fulvenallene in TMC-1 with the QUIJOTE line survey
• Discovery of two cyano derivatives of acenaphthylene (C${}_{12}$H${}_8$) in TMC-1 with the QUIJOTE line survey
• A new protonated molecule discovered in TMC-1: HCCNCH+
• Discovery of five cyano derivatives of propene with the QUIJOTE line survey
• Laboratory and astronomical discovery of the cyanovinyl radical H2CCCN
• CN and CCH derivatives of ethylene and ethane: Confirmation of the detection of CH${}_3$CH${}_2$CCH in TMC-1