Low-temperature formation of polycyclic aromatic hydrocarbons in Titan’s atmosphere

@article{Zhao2018LowtemperatureFO,
  title={Low-temperature formation of polycyclic aromatic hydrocarbons in Titan’s atmosphere},
  author={Long Zhao and Ralf I. Kaiser and Bo Xu and Utuq Ablikim and Musahid Ahmed and Mikhail M. Evseev and Eugene K. Bashkirov and Valeriy N. Azyazov and Alexander Moiseevich Mebel},
  journal={Nature Astronomy},
  year={2018},
  volume={2},
  pages={973-979}
}
The detection of benzene in Titan’s atmosphere led to the emergence of polycyclic aromatic hydrocarbons (PAHs) as potential nucleation agents triggering the growth of Titan’s orange-brownish haze layers. However, the fundamental mechanisms leading to the formation of PAHs in Titan’s low-temperature atmosphere have remained elusive. We provide persuasive evidence through laboratory experiments and computations that prototype PAHs like anthracene and phenanthrene (C14H10) are synthesized via… 
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References

SHOWING 1-10 OF 80 REFERENCES

Low temperature formation of naphthalene and its role in the synthesis of PAHs (Polycyclic Aromatic Hydrocarbons) in the interstellar medium

It is shown that naphthalene can be formed in the gas phase via a barrierless and exoergic reaction between the phenyl radical (C6H5) and vinylacetylene (CH2 = CH-C ≡ CH) involving a van-der-Waals complex and submerged barrier in the entrance channel.

Mechanisms of formation of nitrogen-containing polycyclic aromatic compounds in low-temperature environments of planetary atmospheres: a theoretical study.

Ab initio quantum chemical calculations of potential energy surfaces for various reaction mechanisms of incorporation of nitrogen atoms into aromatic rings of polycyclic aromatic compounds, which may lead to the formation of N-PACs under the low-temperature and low-pressure conditions of Titan's atmosphere are carried out.

Mechanisms for the formation of benzene in the atmosphere of Titan

[1] Polycyclic aromatic hydrocarbons (PAHs) are important interstellar species, and their precursor benzene (C6H6) has been detected in our solar system. In this study the possibility of benzene…

The photochemical products of benzene in Titan’s upper atmosphere

Unexpected chemistry from the reaction of naphthyl and acetylene at combustion-like temperatures.

Experimental evidence indicates that the HACA mechanism does not lead to cyclization of the third aromatic ring as expected but rather undergoes ethynyl substitution reactions instead.

Polycyclic aromatic hydrocarbons in the atmospheres of Titan and Jupiter.

Incompletely characterized complex organic solids (tholins) produced by irradiating simulated Titan atmospheres reproduce well the observed UV/visible/IR optical constants of the Titan stratospheric haze.

Hydrogen-Abstraction/Acetylene-Addition Exposed.

This study provides the first solid experimental evidence on the facile formation of naphthalene in a simulated combustion environment validating the previously postulated HACA mechanism for these two radicals.

Nitrile gas chemistry in Titan's atmosphere

HACA's Heritage: A Free-Radical Pathway to Phenanthrene in Circumstellar Envelopes of Asymptotic Giant Branch Stars.

By exploring the previously unknown chemistry of the ortho-biphenylyl radical with acetylene, this work delivers compelling evidence on the efficient synthesis of phenanthrene in carbon-rich circumstellar environments and implies that HACA alone cannot be responsible for the formation of PAHs in extreme environments.

THE INFLUENCE OF BENZENE AS A TRACE REACTANT IN TITAN AEROSOL ANALOGS

Benzene has been detected in Titan's atmosphere by Cassini instruments, with concentrations ranging from sub-ppb in the stratosphere to ppm in the ionosphere. Sustained levels of benzene in the haze…
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