PRESENT STATUS OF METHANE SPECTROSCOPY FOR PLANETARY APPLICATIONS

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PRESENT STATUS OF METHANE SPECTROSCOPY FOR
PLANETARY APPLICATIONS

• Vincent BOUDON1, Andrei NIKITIN2, Jean-Paul
  CHAMPION1,
• Michel LOETE1, Christian WENGER1
• 1 Institut Carnot de Bourgogne UMR 5209
  CNRS-Université de Bourgogne, 9 Av. A. Savary, BP
  47870, F-21078 DIJON, France
• 2 Laboratory of Theoretical Spectroscopy,
  Institute of Atmospheric Optics, Russian Academy
  of Sciences, 634055 Tomsk, Russia

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Methane everywhere !
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Contents

• The absorption spectrum of methane
• Present status of CH4 spectroscopy
• Recent results concerning Titan
• Perspectives for CH4 spectroscopy

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I. The absorption spectrum of methane
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The methane molecule
Normal modes of methane
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The polyads of CH4
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CH4 complexity Octad levels and mixings
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Tensorial formalism
Systematic expansion of effective Hamiltonian and
transition moment up to any order and for any
polyad scheme, thanks to group theory and
tensorial methods

• All interactions are automatically included
• Vibrational extrapolation
• Global analyses

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II. Present status of CH4 spectroscopy
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Present status of CH4 analyses
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Global fit of the 04800 cm-1 region
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The Octad spectrum at 78 K (res. 0.001 cm-1)
Calc.
Exp.
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Comparison with previous results
Old Calc. (Hilico et al.)
New Calc.
Exp.
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Octad intensities
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III. Recent results concerning Titan
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3 ?m region with ISO spectra
12CH4 13CH4 12CH3D absorption coefficients
calculated thanks to Dijon analyses Modeling of
ISO Keck II data, including haze profile
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Surface albedo from CFHT/FTS spectra
2 ?m window
?2
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VLT/NACO spectrum of Huygens site
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Evidence of a polar ethane cloud
C. A. Griffith, P. Penteado, P. Rannou,R. Brown,
V. Boudon, K. H. Baines,R. Clark, P. Drossart,
B. Buratti,P. Nicholson, C. P. McKay, A.
Coustenis, A. Negrão and R. Jaumann,Science
313, 16201622 (2006)
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IV. Perspectives for CH4 spectroscopy
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Spectroscopy of CH4 what next?
Continue the global analysis approach Next
goals Tetradecad (5400 6300 cm-1), Icosad,
Add new data (positions intensities, hot
bands) Windows (high J, far wings)
Experiments in Grenoble New approches Use
of the ab initio potential energy surface to
derive the effective Hamiltionian and dipole
moment (cf. work of Vl. G. Tyuterev, Reims,
France) Statistical approach for hot bands
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The STDS software
Spherical Top Data System http//icb.u-bourgogne
.fr/OMR/SMA/SHTDS Molecular parameter
database Calculation and analysis programs
XTDS Java interface