Analyse Globale du Spectre de 12CH4 dans la Région 0–4800 cm-1

Statut Actuel et Perspectives Concernant l'Analyse Raie par Raie du Spectre du Méthane

Global analysis of 13CH4 lines in the 0 - 3200 cm-1 region

We have carried out new measurements of infrared spectra of the spherical top molecules 12CH4, 13CH4 and 12CD4 at low – (80K) and room temperature (298K). Spectra were recorded at very high resolution (0.0027 cm−1 around 2900 cm−1) using the Z¨urich prototype Bruker 125 spectrometer (ZP 2001)3 combined with a low temperature cooling cell. Due to low temperature, the Doppler full width at half maximum (0.0045 cm−1 around 2900 cm−1 at 80K) was reduced by a factor of 1.91. We report the analysis of two low – and six room temperature spectra and present the global analysis of 4000 (2000 newly assigned) 13CH4-transitions from 0 up to 3200 cm−1. The results are compared to previous work. In the p…

Global Frequency and Infrared Intensity Analysis of 12CH4 in the 0–4800 cm-1 Region

Simulation de spectres à haute température : une approche statistique du compromis résolution / précision

International audience; Malgré les progrès continus enregistrés dans le domaine de la spectroscopie moléculaire, théorique et expérimentale, les banques de données spectroscopiques disponibles présentent des lacunes importantes, notamment pour l'interprétation des observations des environnements astrophysiques à haute température. Ce constat s'applique en particulier à la molécule de méthane présente dans les atmosphères de nombreux objets astrophysiques. La modélisation du coefficient d'absorption du méthane dans le proche infrarouge et/ou à haute température continue à défier les théoriciens du fait de la complexité intrinsèque de son spectre rovibrationnel. De fait, les analyses à haute …

Global Analysis of 13CH4 Lines in the 0–3200 cm-1 Region

The present status of methane spectroscopy for planetary applications

International audience

Multi-resolution error analysis of predicted absorption coefficients. Method and computer implementation. Application to the IR spectrum of methane at high temperature.

A general method for the estimation of the confidence interval of molecular absorption coefficients is presented. It combines statistical numerical experiments with analytical calculations. The method uses line parameter predictions (position and intensity) with known estimated uncertainties. The propagation of errors from line parameters to absorption coefficients or cross-sections are analyzed in detail as a function of the resolution. This work is especially intended to provide expert information for applications requiring theoretical predictions for which the present state of the art of line by line high-resolution modeling is not accurate enough to meet the experimental precision. As a…

Theoretical background and preliminary results of the global modeling of the lower three polyads of PH3 covering the 3 to 10 µm spectral region

A recent study reported in 2006 provided an empirical database of PH3 (line positions and intensities) in the 3 μm region. The study was based experimentally on FTIR spectra recorded at Kitt Peak at various optical densities and theoretically on single state fits of features assigned using the ground state combination differences method. The need for a complete analysis of the octad was underlined in order to account for the complex interactions which is expecially important for intensity modeling. The polyad pattern of the PH3 molecule presents close similarities with those of spherical top molecules (like CH4), although the symmetry degeneracies are reduced. The simultaneous analysis of t…

The STDS Dijon system : Present status and prospects.

The Dijon spectroscopy group has developed powerful techniques based on group theory and tensorial formalism in order to analyze and simulate absorption and Raman spectra of molecules with various symmetries. Software packages and databases implementing these tools have been created [1]. Compared to the widely used spectroscopic databases (HITRAN, GEISA), these packages, with their XTDS common interface [2], are primarily devoted to the calculation of line parameters and spectra from a database of model parameters. Future developments include improved fitting algorithms, inclusion of C3v symmetric tops, rovibronic couplings, uncertainty estimates. Moreover, calculated line lists will be acc…

The 2200–4700 cm-1 Strong Interaction Region of 13CH4

Analysis of the High Resolution IR-Spectrum of 13CH4 in the 2200–4700 cm-1 Region The Pentad and the Octad

Global Frequency and Infrared Intensity Analysis of 12CH4 Lines in the 900–4800 cm-1 Region

Multi-Resolution error analysis of predicted absorption coefficients. Method and computer implementation. Application to the infrared spectrum of methane at high temperature.

A general method for the estimation of the confidence interval of molecular absorption coefficients is presented. It combines statistical numerical experiments with analytical calculations. The method uses line parameter predictions (position and intensity) with known estimated uncertainties. The propagation of errors from line parameters to absorption coefficients or cross-sections are analyzed in detail as a function of the resolution. This work is especially intended to provide expert information for applications requiring theoretical predictions for which the present state of the art of line by line high-resolution modeling is not accurate enough to meet the experimental precision. As a…