6533b859fe1ef96bd12b74c0
RESEARCH PRODUCT
Multi-resolution investigations of the methane IR spectrum. At the borderline between modelling state of the art and astrophysical needs
Jean-paul Championsubject
cross-section[PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph][ PHYS.PHYS.PHYS-AO-PH ] Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]multi-resolutionconfidence intervalmethaneabsorption coefficient[PHYS.PHYS.PHYS-AO-PH] Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]description
International audience; Remote sensing of the atmosphere of astrophysical objects relies essentially on molecular spectroscopy. Astrophysical investigations generally need both complete and accurate spectroscopic databases. Despite continuous efforts in experimental and theoretical spectroscopic investigations, the lack of data in specific spectral regions of interest is one of the principal limitation of the presently available spectroscopic databases. Extrapolations to relevant experimental conditions like high temperature is also a major issue for astrophysical applications. Among other molecules, methane is present in the atmosphere of many astrophysical objects. The modeling of its absorption coefficient in the near infrared and/or at high temperature remains a challenge mainly because of the intrinsic complexity of its ro-vibrational spectrum. Global effective models, introduced very early, were successfully applied to provide a unified description of the successive lower polyads of the molecule. Unfortunaltely, the extremely large density of levels in highly excited polyads make it very difficult (if not to say impossible) to envisage line by line modeling above say 10 000 cm-1. In fact, the present state of the art of high-resolution modeling is limited approximately to the spectral region below around 5 000 cm-1 (see [1] and references therein). It is very likely that high-resolution line by line modeling up to 10 000 cm-1 will take several years. The talk will be focused on multi-resolution approaches especially designed for astrophysical applications for which the completeness and the reliability of spectroscopic data is at least as important as the resolution itself. The interest of low resolution investigations based on low order expansions of global effective polyad hamiltonians and transition moment operators will be discussed. By fitting observed data including band profils or ab initio results such models may provide usefull information in situations where a gap exists between astrophysical needs and the present state of the art of spectroscopic modeling. Illustrations will be presented about high temperature methane : (i) improved partition sum calculation of methane at high temperature [2]; (ii) advanced statistical error analysis of multi-resolution absorption predictions involving hot band systems arising from highly excited states [3]. References 1. S. Albert, et al., Chem. Phys. 356, 131-146 (2009) 2. C. Wenger, J.P. Champion, V. Boudon, J.Q.S.R.T.. 109, 2697-2706 (2008), http://hal.archives-ouvertes.fr/hal-00277904/fr/ 3. C. Wenger, J.P. Champion, in preparation.
year | journal | country | edition | language |
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2009-07-05 |