THE {nu}{sub 8} BENDING MODE OF DIACETYLENE: FROM LABORATORY SPECTROSCOPY TO THE DETECTION OF {sup 13}C ISOTOPOLOGUES IN TITAN'S ATMOSPHERE

Journal Article · Sat May 01 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/714/1/852· OSTI ID:21448862

Jolly, A; Benilan, Y ^[1]; Fayt, A ^[2]; Jacquemart, D ^[3]; Nixon, C A ^[4]; Jennings, D E ^[5]

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1. LISA, Universite Paris 7 et 12, UMR 7583 du CNRS, 61 Avenue du General de Gaulle, 94010 Creteil Cedex (France)
2. Laboratoire de Spectroscopie Moleculaire, Universite Catholique de Louvain, Chemin du cyclotron 2, B-1348 Louvain-la-Neuve (Belgium)
3. LADIR, Universite Paris 6, UMR 7075 du CNRS, Bat F 74, 4 Place Jussieu, 75252 Paris 05 (France)
4. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
5. NASA, Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

The strong {nu}{sub 8} band of diacetylene at 627.9 cm{sup -1} has been investigated to improve the spectroscopic line data used to model the observations, particularly in Titan's atmosphere by Cassini/Composite Infrared Spectrometer. Spectra have first been recorded in the laboratory at 0.5 and 0.1 cm{sup -1} resolution and temperature as low as 193 K. Previous analysis and line lists present in the GEISA database appeared to be insufficient to model the measured spectra in terms of intensity and hot band features. To improve the situation and in order to be able to take into account all rovibrational transitions with a non-negligible intensity, a global analysis of C{sub 4}H{sub 2} has been carried out to improve the description of the energy levels up to E{sub v} = 1900 cm{sup -1}. The result is a new extensive line list which enables us to model very precisely the temperature variation as well as the numerous hot band features observed in the laboratory spectra. One additional feature, observed at 622.3 cm{sup -1}, was assigned to the {nu}{sub 6} mode of a {sup 13}C isotopologue of diacetylene. The {nu}{sub 8} bands of both {sup 13}C isotopomers were also identified in the 0.1 cm{sup -1} resolution spectrum. Finally, a {sup 13}C/C{sub 4}H{sub 2} line list was added to the model for comparison with the observed spectra of Titan. We obtain a clear detection of {sup 13}C monosubstituted diacetylene at 622.3 cm{sup -1} and 627.5 cm{sup -1} (blended {nu}{sub 8} bands), deriving a mean {sup 12}C/{sup 13}C isotopic ratio of 90 {+-} 8. This value agrees with the terrestrial (89.4, inorganic standard) and giant planet values (88 {+-} 7), but is only marginally consistent with the bulk carbon value in Titan's atmosphere, measured in CH{sub 4} by Huygens GCMS to be 82 {+-} 1, indicating that isotopic fractionation during chemical processing may be occurring, as suggested for ethane formation.

• OSTI ID: 21448862
• Journal Information: Astrophysical Journal, Vol. 714, Issue 1; Other Information: DOI: 10.1088/0004-637X/714/1/852; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CARBON 12
CARBON 13
ETHANE
FRACTIONATION
GLOBAL ANALYSIS
INFRARED SPECTROMETERS
ISOTOPE RATIO
METHANE
PLANETS
SATELLITE ATMOSPHERES
SATELLITES
SPECTROSCOPY
ALKANES
ATMOSPHERES
CARBON ISOTOPES
DIMENSIONLESS NUMBERS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HYDROCARBONS
ISOTOPES
LIGHT NUCLEI
MATHEMATICS
MEASURING INSTRUMENTS
NUCLEI
ORGANIC COMPOUNDS
SEPARATION PROCESSES
SPECTROMETERS
STABLE ISOTOPES