The spatial distribution of an aromatic molecule, C<sub>6</sub>H<sub>5</sub>CN, in the cold dark cloud TMC-1

Cernicharo, J.; Tercero, B.; Marcelino, N.; Agúndez, M.; Vicente, P. de

doi:10.1051/0004-6361/202346722

Cited by 12 publications

(1 citation statement)

References 26 publications

(34 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Top-down approaches have been suggested to be responsible for the large abundance of aromatics in TMC-1 (Burkhardt et al 2021b), which might be inherited from a previous diffuse phase. On the other hand, the recent discovery of 1-cyano-1,3-butadiene (C 4 H 5 CN; Cooke et al 2023) and the spatial distribution of C 6 H 5 CN (Cernicharo et al 2023) have been used to argue that the formation of aromatics proceeds through bottom-up chemical routes.…”

Section: Discussionmentioning

confidence: 99%

Photocleavage of Aliphatic C–C Bonds in the Interstellar Medium

Tajuelo-Castilla,

Mendieta-Moreno,

Accolla

et al. 2024

ApJ

View full text Add to dashboard Cite

Ultraviolet (UV) processing in the interstellar medium (ISM) induces the dehydrogenation of hydrocarbons. Aliphatics, including alkanes, are present in different interstellar environments, being prevalently formed in evolved stars; thus, the dehydrogenation by UV photoprocessing of alkanes plays an important role in the chemistry of the ISM, leading to the formation of unsaturated hydrocarbons and eventually to aromatics, the latter ubiquitously detected in the ISM. Here, through combined experimental results and ab initio calculations, we show that UV absorption (mainly at the Lyα emission line of hydrogen at 121.6 nm) promotes an alkane to an excited Rydberg state from where it evolves toward fragmentation, inducing the formation of olefinic C=C bonds, which are necessary precursors of aromatic hydrocarbons. We show that the photochemistry of aliphatics in the ISM does not primarily produce direct hydrogen elimination but preferential C–C photocleavage. Our results provide an efficient synthetic route for the formation of unsaturated aliphatics, including propene and dienes, and suggest that aromatics could be formed in dark clouds by a bottom-up mechanism involving molecular fragments produced by UV photoprocessing of aliphatics.

show abstract

Section: Discussionmentioning

confidence: 99%

Photocleavage of Aliphatic C–C Bonds in the Interstellar Medium

Tajuelo-Castilla,

Mendieta-Moreno,

Accolla

et al. 2024

ApJ

View full text Add to dashboard Cite

show abstract

A computational characterization of the reaction mechanisms for the reactions N(2D) + CH3CN and HC3N and implications for the nitrogen-rich organic chemistry of Titan

Mancini,

Rosi,

Skouteris

et al. 2023

Computational and Theoretical Chemistry

View full text Add to dashboard Cite

Abundance and excitation of molecular anions in interstellar clouds

Agúndez¹,

Marcelino²,

Tercero³

et al. 2023

A&A

View full text Add to dashboard Cite

We present new observations of molecular anions with the Yebes 40 m and IRAM 30 m telescopes toward the cold, dense clouds TMC-1 CP, Lupus-1A, L1527, L483, L1495B, and L1544. We report the first detections of C3N− and C5N− in Lupus-1A as well as C4H− and C6H− in L483. In addition, we detected new lines of C6H− toward the six targeted sources, of C4H− toward TMC-1 CP, Lupus-1A, and L1527, and of C8H− and C3N− in TMC-1 CP. Excitation calculations using recently computed collision rate coefficients indicate that the lines of anions accessible to radiotelescopes run from subthermally excited to thermalized as the size of the anion increases, with the degree of departure from thermalization depending on the H2 volume density and the line frequency. We noticed that the collision rate coefficients available for the radical C6H are not sufficient to explain various observational facts, thereby calling for the collision data for this species to be revisited. The observations presented here, together with observational data from the literature, have been used to model the excitation of interstellar anions and to constrain their abundances. In general, the anion-to-neutral ratios derived here agree with the literature values, when available, within 50% (by a factor of two at most), except for the C4H−/C4H ratio, which shows higher differences due to a revision of the dipole moment of C4H. From the set of anion-to-neutral abundance ratios derived two conclusions can be drawn. First, the C6H−/C6H ratio shows a tentative trend whereby it increases with increasing H2 density, as we would expect on the basis of theoretical grounds. Second, the assertion that the higher the molecular size, the higher the anion-to-neutral ratio is incontestable; furthermore, this supports a formation mechanism based on radiative electron attachment. Nonetheless, the calculated rate coefficients for electron attachment to the medium size species C4H and C3N are probably too high and too low, respectively, by more than one order of magnitude.

show abstract

The spatial distribution of an aromatic molecule, C₆H₅CN, in the cold dark cloud TMC-1

Cited by 12 publications

References 26 publications

Photocleavage of Aliphatic C–C Bonds in the Interstellar Medium

Photocleavage of Aliphatic C–C Bonds in the Interstellar Medium

A computational characterization of the reaction mechanisms for the reactions N(2D) + CH3CN and HC3N and implications for the nitrogen-rich organic chemistry of Titan

Abundance and excitation of molecular anions in interstellar clouds

Contact Info

Product

Resources

About

The spatial distribution of an aromatic molecule, C6H5CN, in the cold dark cloud TMC-1

Cited by 12 publications

References 26 publications

Photocleavage of Aliphatic C–C Bonds in the Interstellar Medium

Photocleavage of Aliphatic C–C Bonds in the Interstellar Medium

A computational characterization of the reaction mechanisms for the reactions N(2D) + CH3CN and HC3N and implications for the nitrogen-rich organic chemistry of Titan

Abundance and excitation of molecular anions in interstellar clouds

Contact Info

Product

Resources

About

The spatial distribution of an aromatic molecule, C₆H₅CN, in the cold dark cloud TMC-1