Titan Haze: Structure and Properties of Cyanoacetylene and Cyanoacetylene–Acetylene Photopolymers

Clarke, D.W.; Ferris, James P.

doi:10.1006/icar.1996.5667

Cited by 87 publications

(69 citation statements)

References 41 publications

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“…The generated HCCN radical species at 60 nm irradiation is most likely lost through subsequent chemical reactions. Nondetection of ðC þ NÞ 4 nitriles species in the gas phase at 60 nm does not support the proposed bimolecular reactions (15,18,29) (Table 1) as the major HCCN loss channels in our experimental condition. The competition of gas-phase and heterogeneous reactions can be discussed by introducing γ, a reaction probability, and ν coll , a collision frequency at the product aerosol substrate/chamber wall (SI Text).…”

Section: Resultscontrasting

confidence: 57%

“…Most UV photochemical investigations for nitrogenated organics have been restricted to studies using HCN and HC 3 N in the initial gas mixtures (18,20). Therefore, the role of Nð 2 DÞ atoms from N 2 molecules in the subsequent complex chemistry is largely unknown.…”

mentioning

confidence: 99%

“…The thick dashed box contains the stable CN-unit species of heavy nitriles ðC þ NÞ 4 (HC 3 N, C 2 H 3 CN, and C 2 N 2 ) observed in Titan's atmosphere. Hypothetical chemical pathways toward nitrogenated organic aerosols, in double arrows, are also shown (14,16); (I) HCN nitrile polymer (19), (II) R-CN nitrile heteropolymers (19), (III) Copolymers (18), and (IV) CH 2 NH imine polymer (14). Among each mechanism (II) and (III), the dominant channels (17) are shown as examples.…”

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confidence: 99%

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Formation of nitrogenated organic aerosols in the Titan upper atmosphere

Imanaka

Smith

2010

Proc. Natl. Acad. Sci. U.S.A.

107

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Many aspects of the nitrogen fixation process by photochemistry in the Titan atmosphere are not fully understood. The recent Cassini mission revealed organic aerosol formation in the upper atmosphere of Titan. It is not clear, however, how much and by what mechanism nitrogen is incorporated in Titan's organic aerosols. Using tunable synchrotron radiation at the Advanced Light Source, we demonstrate the first evidence of nitrogenated organic aerosol production by extreme ultraviolet-vacuum ultraviolet irradiation of a N 2 ∕CH 4 gas mixture. The ultrahigh-mass-resolution study with laser desorption ionization-Fourier transform-ion cyclotron resonance mass spectrometry of N 2 ∕CH 4 photolytic solid products at 60 and 82.5 nm indicates the predominance of highly nitrogenated compounds. The distinct nitrogen incorporations at the elemental abundances of H 2 C 2 N and HCN, respectively, are suggestive of important roles of H 2 C 2 N∕HCCN and HCN∕CN in their formation. The efficient formation of unsaturated hydrocarbons is observed in the gas phase without abundant nitrogenated neutrals at 60 nm, and this is confirmed by separately using 13 C and 15 N isotopically labeled initial gas mixtures. These observations strongly suggest a heterogeneous incorporation mechanism via short lived nitrogenated reactive species, such as HCCN radical, for nitrogenated organic aerosol formation, and imply that substantial amounts of nitrogen is fixed as organic macromolecular aerosols in Titan's atmosphere.

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Section: Resultscontrasting

confidence: 57%

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confidence: 99%

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confidence: 99%

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Formation of nitrogenated organic aerosols in the Titan upper atmosphere

Imanaka

Smith

2010

Proc. Natl. Acad. Sci. U.S.A.

107

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“…. Polymerization processes proposed for HC 5 N photochemistry at longer wavelength photons (>300 nm), based on the scheme proposed by Clarke & Ferris (1997) for HC 3 N polymerization. Based on the infrared spectra, we propose possible structures for HC 5 N polymers.…”

Section: Infrared Spectrum Of the Hc 5 N Residuementioning

confidence: 99%

Simulation of Titan’s atmospheric photochemistry

Couturier-Tamburelli

Piétri

Gudipati

2015

A&A

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We studied the photochemistry of frozen ice of a polar Titan's atmospheric molecule cyanodiacetylene (HC 5 N) to determine the possible contribution of this compound to the lower altitude photochemistry of haze layers found on Titan. We used infrared analysis to examine the residue produced by irradiation of solid HC 5 N at λ > 300 nm. The resulting polymer is orange-brown in color. Based on theoretical analysis and the general tendency of HC 5 N and C 4 N 2 to undergo similar ice photochemistry at longer wavelengths accessible in Titan's lower atmosphere, we conclude that Titan's lower atmosphere is photochemically active in the regions of cloud, ice, and aerosol formation. C 4 N 2 is a symmetric molecule with no net dipole moment whereas, HC 5 N has a large dipole moment of ∼4 D. Consequently, though both these molecules have very similar molecular weight and size, their sublimation temperatures are different, HC 5 N subliming around 170 K compared to 160 K for C 4 N 2 . Based on our studies we conclude that in Titan's atmosphere the cyanoacetylene class of molecules (HCN, HC 3 N, HC 5 N, etc.) would condense first followed by the dicyanoacetylenes (C 2 N 2 , C 4 N 2 , C 6 N 2 , etc.), leading to fractionation of different class of molecules. From the fluxes used in the laboratory and depletion of the original HC 5 N signals, we estimate Titan's haze ice photochemistry involving polar nitriles to be significant and very similar to their non-polar counterparts.

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“…21 Several limitations such as wall effects undermine their validity. 22 Also, the reaction products are often analyzed off-line and ex situ. 23 Hence, the detailed chemical dyna- ) 17 with unsaturated hydrocarbons demonstrated that highly unsaturated nitriles -organic molecules carrying the cyano (CN) group -and hydrogen-deficient molecules, among them (substituted) polyynes up to triacetylene, can be formed ( Figure 1).…”

Section: Introductionmentioning

confidence: 99%