Axis 3: From laboratory spectroscopy to the study of the universe

Our skills in experimental and theoretical spectroscopy enable us to contribute to answering various questions related to observations of the universe since most of the molecules that we study are of atmospheric, interstellar, and pre-biotic interest... We thus provide spectroscopic parameters of these molecules through international databases in a manner useful to the scientific community and when possible, we assess the impact of our results on simulations and treatments of atmospheric and astrophysical spectra.

(A) Studied molecules

- Various molecules of atmospheric interest (earth and planets) are studied in order to improve the accuracy of the existing spectral data or to provide the first existing data set (ex: O3, H2CO, HCOOH, HNO3, HONO, H2O, SO2, HC3N, CH3CN, C4H2, HC3N, C3H8, C2H6, 13CH3D, NH3, CH4, CO2, O2, N2, HCl, HF, CH3F, NH3, FCO2, COFCl, CH3Br, CH3Cl…)

- Various molecules detected in the interstellar medium are studied in order to prepare future observations with instruments that will be unsurpassed in both accuracy and extent of the spectral range, like the radio telescopes HIFI/Herschel & ALMA or the stratosphere based IR observatory SOFIA . These molecules include CH3COOH, HCOOCH3 and its isotopes, CH2DOH, CH3COD, CH3CONH2, CH2DCONH2, 15NH2D and 15ND2H...

- Prebiotics and biomimetic molecules: in addition to their astrophysical and exobiological interest, some simple biomolecules can be considered as biomimetic. This biomimetic concept consists of reducing the size of the molecular system (which allows to study it by high resolution spectroscopy) to an elementary brick (amino acid, small peptide, simple ester...) which mimics particular properties of larger biological structures. Such spectroscopic studies in the dilute phase are used to validate quantum chemistry calculations of small molecules of biological interest and to provide structural, conformational or photochemical data used as a "benchmark" for the study of larger systems (alanine dipeptide, organic esters, acetamide, etc).

(B) Building up spectroscopic databases

Our spectroscopic studies and results largely feed spectroscopic databases (DB) with data such as the line positions and intensities and parameters for the description of the effects of pressure. These databases may be "general" (HITRAN$, GEISA$, MIPAS$, JPL$, CDMS$, SPLATALOGUE$...) or dedicated to a specific instrument (MIPAS$, GOSAT$). An example of improvement of the GEISA& DB is given by the figure below for formaldehyde (H2CO). For this molecule, some intercalibrated measurments were carried out in the laboratory with the simultaneous determination, for the first time, of formaldehyde absorption cross sections of in the UV and IR spectral regions.



Fig. 2 (a) Improvement of the GEISA-ETHER/HITRAN database thanks to the line list built at LISA (a) (blue) that improves the previous work (red). Note that there were no data available in the 100-1800 cm - 1 region before our work; (b) first determinations of the atmospheric H2CO vertical profile by the satellite instrument MIPAS in the 5.7 m region, a result made possible by the LISA line llist (Steck et al. 2008).

(C) Validation and consequences of the laboratory studies by and for atmospheric and astrophysical spectra

Atmospheric spectra are also used to test the tools and data derived from our spectroscopic research. An example is formaldehyde, whose vertical profile was measured for the first time thanks to the LIS1A line list (fig.2). Detections of isotopomers of HCOOCH3 or of deuterated ammonia in the Orion molecular cloud, which were also made possible by our modeling, also illustrate the consequences and interest of our spectroscopic studies (Fig.3).

First detection of methyl formaldehyde H13COOCH3 in the the Orion molecular cloud by the IRAM telescope [Carvajal et al 2009], through modeling of the microwave spectrum made at LISA. Observed spectrum (in black) compared to the modeling of the lines of type A (in red).

Far infrared spectrum of 15NH2D and 15ND2H species measured at LISA in red, calculated spectrum in blue, (Elkeurti et al. 2008). This work enabled the first detection of 15NH2D, in dense interstellar clouds Barnard-1B and L1689N (Gerin et al 2009). These studies enable to set constraints on the 13 c/12 c et15N/14N isotope ratios.

It has also been possible to demonstrate the importance of taking into account some collisional effects for proper treatments of atmospheric spectra. This is a crucial step before releasing our models and data in the community of atmospheric scientists. For this, inversions of atmospheric spectra were carried out to assess the consequences of our results on remote sensing of vertical profiles of some gases, of CO2 columns, and of pressure field. An example is given in the following figure for CO2, where the sinks and sources are the targets of the satellite projects "Orbiting Carbon Observatory" (OCO) and "Greenhouse gases Observation SATellite" (GOSAT).

Fig.4. Influence of collisional interference between CO2 lines (Line-Mixing) near 2.1 m, one of the regions retained by the OCO and GOSAT satellites to determine the columns of CO2 in the atmosphere [Hartmann, Ha et al, 2009].


Let us finally mention some simulations of spectra recorded by the spectrometer SRTC & onboard the Cassini in order to obtain reliable values of the abundances of C3H8, 13CH3D, or even C4H2 and HC3N in the atmosphere of Titan. Such studies involve collaborations between experimentalists, theoreticians and planetologists.