Atmosphere of Titan

Diacetylene (HC=C—C=CH) has been identified as a component of the hydrocarbon rich atmospheres of Uranus Neptune and Pluto It is also present m the atmospheres of Titan and Triton satellites of Saturn and Neptune respectively... 

These new results only became possible when the groups of H. Waite and B. Magee at the South West Research Institute (SWRI) in San Antonio, Texas, combined analytical data obtained from two different instruments. These are the ion and neutral mass spectrometer (INMS), which obtained data on small to medium-sized molecules in the upper atmosphere of Titan (950-1,150 km) and the Cassini plasma spectrometer (CAPS), which also registered particles from tholins, both positive (100-350 Da) and negative ions (20-8,000 Da) (Waite et al., 2007 Atrey, 2007). 

Essentially, all reactions that require the formation of a chemical bond with an activation energy of around 100 kJ mol-1 are frozen out at the surface of Titan but are considerably faster in the stratosphere, although still rather slow compared with the rates of reaction at 298 K. Chemistry in the atmosphere of Titan will proceed slowly for neutral reactions but faster for ion-molecule reactions and radical-neutral reactions, both of which have low activation barriers. The Arrhenius equation provides the temperature dependence of rates of reactions but we also need to consider the effect of cold temperatures on thermodynamics and in particular equilibrium. 

It is clear that a complex hydrocarbon polymer chemistry must exist in the atmosphere of Titan involving polyyne species, polynitrile species and mixtures of the two, and additional routes to polyaromatic hydrocarbon formation. This presents a significant problem for the gas chromatography/mass spectrometry instruments on the Huygens probe. There should be hydrocarbon fragments, producing perhaps... 

Yi-Jehng Kuan el al. (2004). Searches for interstellar molecules of potential prebiotic importance. Advances in Space Research 33 31-39 Yung Y., Allen M. and Pinto J. (1984). Photochemistry of the atmosphere of Titan comparison between model and observations. Astronomy Astrophysics Supplement... 

Lutz B. L., Debergh C., and Owen T. (1983a) Carbon-monoxide in the atmosphere of Titan—search and discovery. Publ. Astron. Soc. Pacific 95, 593—593. 

In contrast, Zahnle et al. [116] argued tliat the present atmosphere of Titan was delivered by comets of low velocity at late accretion, ai d Uiat Titan has suffered less atmospheric erosion and has retained a higher fraction of incoming atmophiles. For a more-or-less solar composition comet, the most important C-and N-bearing products are likely CO and N2, witli small additional amounts of CO2, CH4, C2H2, and HCN. Most of the comet s N2 entered the atmosphere on Titan, where CO has been consumed by reaction with water to form CO2, CH4, and H2, the latter readily escaping into space. This alternative model for the formation of the present day atmosphere on Titan does not require conversion of N2 from NH3. 

Raulin, F. Accaoui, B. Razaghi, A. Dang-Nhu, M. Coustenis, A. Gautier, D. Infrared spectra of gaseous organics application to the atmosphere of Titan-II. Infrared intensities and frequencies of C4 alkanenitriles and benzene. Spectrochimica Acta 1990, 46A, 671-683. 

C4H2 isomers are of great interest to astronomers because some of these molecules occur in the atmospheres of Titan [74] (and references therein), Jupiter [75] (and references therein), possibly Pluto [76] in a comet [77], and in circumstellar and interstellar media [42,78-80]. Quantum chemical treatments of the 18 possible constructs, which included branched open constructs, produced 10 molecules of which four were open and six were cyclical. All have singlet ground states. Several investigators have synthesized 4Ol(s) in the gas phase and in solvents. Goldberg et al. [81] have synthesized 4O2(s) in the gas phase. 

CgHz occurs in the atmosphere of Titan [132,133]. The compound was recently synthesized in solutions by Cataldo [1,2], who also determined its UV-vis absorption spectrum. We will consider only the two open molecules... 

Delpech, C. Guillemin, J.C. Paillous, P. Khlifi, M. Bruston, P. Raulin F. Infrared spectra of triacetylene in the 4000-220 cm region absolute band intensity and implications for the atmosphere of Titan. Spectrochim. Acta A 1994, 50, 1095-1100. 

U.v. measurement of the Saturnine atmosphere,242 hydrocarbon abundances on Jupiter,243 and the photochemistry of hydrocarbons in the atmosphere of Titan 344 have been discussed. 

Acrylonitrileundergoes a [2+2] cycloaddition reaction with ketene alkylsilyl acetals. Like cyanoketenes, cyanoacetylenes readily undergo cycloaddition reactions, and research was given an additional stimulus by their observation in the atmosphere of Titan. ... 

Wilson, E. H. and S. K. Atreya (2000) Sensitivity studies of methane photolysis and its impact on hydrocarbon chemistry in the atmosphere of Titan. Journal of Geophysical Research 105, 20263-20273... 

From data gathered by Voyager 1, scientists have estimated the com- of 82 mol percent N2, 12 mol percent Ar, and 6.0 mol percent CH4. position of the atmosphere of Titan, Saturn s largest moon. The Calculate the partial pressure of each gas. 

Alkanes have the general molecular formula C 2n+i The simplest one, methane (CH4), is also the most abundant. Large amounts are present in our atmosphere, in the ground, and in the oceans. Methane has been found on Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto, and even on Halley s Comet. About 2-8% of the atmosphere of Titan, Saturn s largest moon, is methane. When it rains on Titan, it rains methane. 

Tholins are complex organics that form via photolysis reaction in the atmosphere of Titan, the largest moon of Saturn, which produces a thick reddish-brown haze. As for the material reported here tholin material can be produced in the laboratory by cold plasma discharge in a nitrogen-methane mixture. 

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