Details

Autor(en) / Beteiligte

• Clarke, David W.
• Ferris, James P.

Titel

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

Ist Teil von

• Icarus (New York, N.Y. 1962), 1997-05, Vol.127 (1), p.158-172

Ort / Verlag

Legacy CDMS: Elsevier Inc

Erscheinungsjahr

1997

Quelle

Access via ScienceDirect (Elsevier)

Beschreibungen/Notizen

• The structure and morphological properties of polymers produced photochemically from the UV irradiation of cyanoacetylene and cyanoacetylene mixtures have been examined to evaluate their possible contribution to the haze layers found on Titan. A structural analysis of these polymers may contribute to our understanding of the data returned from the Huygens probe of the Cassini mission that will pass through the atmosphere of Titan in the year 2004. Infrared analysis, elemental analysis, and thermal methods (thermogravimetric analysis, thermolysis, pyrolysis) were used to examine structures of polycyanoacetylenes produced by irradiation of the gas phase HC 3N at 185 and 254 nm. The resulting brown to black polymer, which exists as small particles, is believed to be a branched chain of conjugated carbon–carbon double bonds, which, on exposure to heat, cyclizes to form a graphitic structure. Similar methods of analysis were used to show that when HC 3N is photolyzed in the presence of Titan's other atmospheric constituents (CH 4, C 2H 6, C 2H 2, and CO), a copolymer is formed in which the added gases are incorporated as substituents on the polymer chain. Of special significance is the copolymer of HC 3N and acetylene (C 2H 2). Even in experiments where C 2H 2was absorbing nearly all of the incident photons, the ratio of C 2H 2to HC 3N found in the resulting polymer was only 2:1. Scanning electron microscopy was used to visually examine the polymer particles. While pure polyacetylene particles are amorphous spheres roughly 1 μm in diameter, polycyanoacetylenes appear to be strands of rough, solid particles slightly smaller in size. The copolymer of HC 3N and C 2H 2exhibits characteristics of both pure polymers. This is particularly important as pure polyacetylenes do not match the optical constants measured for Titan's atmospheric hazes. The copolymers produced by the incorporation of other minor atmospheric constituents, like HC 3N, into the polyacetylenes are expected to have optical constants more comparable to those of the Titan haze.