Chemical Characterization of Titan's Tholins: Solubility, Morphology and Molecular Structure Revisited

被引:86
作者
Carrasco, N. [1 ]
Schmitz-Afonso, I. [2 ]
Bonnet, J-Y. [3 ]
Quirico, E. [3 ]
Thissen, R. [3 ]
Dutuit, Odile [3 ]
Bagag, A. [2 ]
Laprevote, O. [2 ]
Buch, A. [4 ]
Giulani, A. [5 ,6 ]
Adande, Gilles [3 ]
Ouni, F. [1 ]
Hadamcik, E. [1 ]
Szopa, C. [1 ]
Cernogora, G. [1 ]
机构
[1] Univ Paris 06, Univ Versailles St Quentin, CNRS, INSU,LATMOS IPSL, F-91371 Verrieres Le Buisson, France
[2] CNRS, Inst Chim Subst Nat, F-91198 Gif Sur Yvette, France
[3] UJF, CNRS, UMR 5109, Lab Planetol Grenoble, F-38041 Grenoble 9, France
[4] Ecole Cent Paris, Lab Genie Proc & Mat, F-92295 Chatenay Malabry, France
[5] SOLEIL, F-91192 Gif Sur Yvette, France
[6] INRA, Cepia, F-44316 Nantes 3, France
关键词
ATMOSPHERIC-PRESSURE PHOTOIONIZATION; HIGH POLYMER-SOLUTIONS; MASS-SPECTROMETRY; THERMODYNAMICS; SIMULATION; PLASMA; HAZE; GAS;
D O I
10.1021/jp904735q
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
In this work Titan's atmospheric chemistry is simulated using a capacitively coupled plasma radio frequency discharge in a N-2-CH4 stationnary flux. Samples of Titan's tholins are produced in gaseous mixtures containing either 2 or 10% methane before the plasma discharge, covering the methane concentration range measured in Titan's atmosphere. We study their solubility and associated morphology, their infrared spectroscopy signature and the mass distribution of the soluble fraction by mass spectrometry. An important result is to highlight that the previous Titan's tholin solubility studies are inappropriate to fully characterize such a heterogeneous organic matter and we develop a new protocol to evaluate quantitatively tholins solubility. We find that tholins contain up to 35% in mass of molecules soluble in methanol, attached to a hardly insoluble fraction. Methanol is then chosen as a discriminating solvent to characterize the differences between soluble and insoluble species constituting the bulk tholins. No significant morphological change of shape or surface feature is derived from scanning electron microscopy after the extraction of the soluble fraction. This observation suggests a solid structure despite an important porosity of the grains. Infrared spectroscopy is recorded for both fractions. The IR spectra of the bulk, soluble, and insoluble tholins fractions are found to be very similar and reveal identical chemical signatures of nitrogen bearing functions and aliphatic groups. This result confirms that the chemical information collected when analyzing only the soluble fraction provides a valuable insight representative of the bulk material. The soluble fraction is ionized with an atmospheric pressure photoionization source and analyzed by a hybrid mass spectrometer. The congested mass spectra with one peak at every mass unit between 50 and 800 u confirm that the soluble fraction contains a complex mixture of organic molecules. The broad distribution, however, exhibits a regular pattern of mass clusters. Tandem collision induced dissociation analysis is performed in the negative ion mode to retrieve structural information. It reveals that (i) the molecules are ended by methyl, amine and cyanide groups, (ii) a 27 tr neutral mnoiety (most probably HCN) is often released in the fragmentation of tholin anions, and (iii) an ubiquitous ionic fragment at 111/7 66 is found in all tandem sp-ectra. A tentative structure is proposed for this negative ion.
引用
收藏
页码:11195 / 11203
页数:9
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