Gas phase dicyanoacetylene (C4N2) on Titan: New experimental and theoretical spectroscopy results applied to Cassini CIRS data

International audienceDicyanoacetylene has not been observed so far in the gas phase in Titan’s atmosphere but this molecule is still on the list of the detected species, on the basis of the correspondence between a solid phase feature measured at 478 cm−1 in the laboratory and a spectral feature observed by Voyager. In this work, the infrared spectrum of gaseous C4N2 has been investigated to improve our knowledge of the band intensities and the line parameters for this molecule. Results of previously investigated bands have been revised and the intensity of the ν9 band at 107 cm−1, measured for the first time, was found to be the strongest absorption in the whole infrared domain. We have also improved the analysis of the complex rotational and hot band structure of C4N2 in order to obtain the first line lists for both bending modes ν8 and ν9. Using our radiative transfer code including the new line list of the strong ν9 band, we have searched for the signature of C4N2 at 107 cm−1 in the atmosphere of Titan utilizing Titan CIRS far infrared spectra. Despite averaging a large number of CIRS spectra at northern latitudes during the very favorable Titan winter, no gaseous C4N2 could be detected. At the 1-σ level we obtain an abundance upper limit of 5.3 × 10−10 for the limb average which is lower than or comparable to previously inferred values. As a consequence, the absence or very low amount of gaseous C4N2 makes quite puzzling its presence in the solid phase with an abundance compatible with the observed spectral feature at 478 cm−

Existence of weak solutions for the generalized Navier-Stokes equations with damping

In this work we consider the generalized Navier-Stokes equations with the presence of a damping term in the momentum equation. The problem studied here derives from the set of equations which govern isothermal flows of incompressible and homogeneous non-Newtonian fluids. For the generalized Navier-Stokes problem with damping, we prove the existence of weak solutions by using regularization techniques, the theory of monotone operators and compactness arguments together with the local decomposition of the pressure and the Lipschitz-truncation method. The existence result proved here holds for any and any sigma > 1, where q is the exponent of the diffusion term and sigma is the exponent which characterizes the damping term.MCTES, Portugal [SFRH/BSAB/1058/2010]; FCT, Portugal [PTDC/MAT/110613/2010]info:eu-repo/semantics/publishedVersio

The 2009 edition of the GEISA spectroscopic database

The updated 2009 edition of the spectroscopic database GEISA (Gestionet Etudedes Informations Spectroscopiques Atmospheriques ; Management and Study of Atmospheric Spectroscopic Information) is described in this paper. GEISA is a computer-accessible system comprising three independent sub-databases devoted, respectively, to: line parameters, infrared and ultraviolet/visible absorption cross-sections, microphysical and optical properties of atmospheric aerosols. In this edition, 50 molecules are involved in the line parameters sub-database, including 111 isotopologues, for a total of 3,807,997 entries, in the spectral range from 10-6 to 35,877.031cm-1. GEISA, continuously developed and maintained at LMD (Laboratoirede Meteorologie Dynamique, France) since 1976, is implemented on the IPSL/CNRS(France) ‘‘Ether’’ Products and Services Centre WEB site (http://ether.ipsl.jussieu.fr), where all archived spectroscopic data can be handled through general and user friendly associated managements of software facilities. More than 350 researchers are registered for online use of GEISA

The Need for Laboratory Measurements and Ab Initio Studies to Aid Understanding of Exoplanetary Atmospheres

Laboratory astrophysics and astrochemistr

New infrared integrated band intensities for HC3N and extensive line list for the v(5) and v(6) bending modes

The infrared spectrum of cyanoacetylene (also called propynenitrile) has been investigated from 400 to 4000 cm(-1) at a resolution of 0.5 cm(-1). Integrated intensities of the main bands and a number of weaker bands have been obtained with an uncertainty better than 5%. Inaccurate values in previous studies have been identified in particular concerning the intensity of the strong nu(5) stretching band at 663.2 cm(-1). Former results on the temperature dependence of integrated intensities have also been revisited. Synthetic spectra calculation has been performed for the nu(5) and nu(6) bands on the basis of the best available high resolution data. It has been shown that the GEISA line parameters for HC3N are not sufficient to reproduce the band intensities and some hot band features observed in our experimental spectra at room temperature. As a first step, the model spectra has been improved by including a number of missing hot subbands and by calculating accurately the hot band relative intensities. Finally, a perfect agreement between calculated and observed spectra was achieved on the basis of a global analysis of HC3N levels up to 2000 cm(-1) combined with the new integrated intensity measurements. A new extensive line list for the nu(5) and nu(6) bending modes of HC3N has been compiled. (c) 2007 Published by Elsevier Inc

HMT production and sublimation during thermal process of cometary organic analogs. Implications for its detection with the ROSETTA instruments

One important component of refractory organic residues synthesized from interstellar/cometary ice analogues is hexamethylenetetramine (HMT, C6H12N4). However, HMT has never been observed in any astrophysical or planetary environment so far. We investigated thermal evolution of HMT above ambient temperature. The synthesis of the organic residue (ice deposition, photolysis and warming) as well as its heating to temperatures higher than 300 K are performed by means of the same experimental apparatus. The later also allows in situ continuous monitoring of both the solid organic residue (by FTIR spectrometry) and of the gas species (by mass spectrometry)

Frequency and intensity analyses of the far infrared nu(5) band system of Cyanogen (C(2)N(2)) and applications to Titan.

The far infrared spectrum of cyanogen has been studied at high resolution to improve the rotational analysis of the ν5 band system around 234 cm−1. Present in the sample in natural abundances, both isotopologues N13CCN and 15NCCN have also been studied. The weak ν4–ν5 difference band centered at 270 cm−1 has been studied for the first time. On the basis of a global rovibrational analysis limited to the ν2, ν4, and ν5 modes, energy levels up to 2300 cm−1 have been considered to contribute to the overall spectrum intensity at room temperature leading to a new line list of 196,994 lines. The line intensity prediction has been used to correct previous line intensity measurements by taking into account line mixing. A new vibrational transition moment has been deduced and compared to new band intensity measurements obtained by low resolution studies which are also presented in this paper. The agreement between both approaches is very good and rules out the apparent disagreement between line intensity and band intensity measurements observed in the past. An intensity study of 15NCCN is also proposed here thanks to the availability of a pure sample. Those results open the way to the search for isotopologues of cyanogen in Titan's atmosphere

The nu(8) bending mode of diacetylene: from laboratory spectroscopy to the detection of (13)C isotopologs in Titan's atmosphere

The strong nu(8) band of diacetylene at 627.9 cm(-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(-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 C4H2 has been carried out to improve the description of the energy levels up to E-v = 1900 cm(-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(-1), was assigned to the nu(6) mode of a C-13 isotopologue of diacetylene. The nu(8) bands of both C-13 isotopomers were also identified in the 0.1 cm(-1) resolution spectrum. Finally, a C-13/C4H2 line list was added to the model for comparison with the observed spectra of Titan. We obtain a clear detection of C-13 monosubstituted diacetylene at 622.3 cm(-1) and 627.5 cm(-1) (blended nu(8) bands), deriving a mean C-12/C-13 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 CH4 by Huygens GCMS to be 82 +/- 1, indicating that isotopic fractionation during chemical processing may be occurring, as suggested for ethane formation