Tholinomics-chemical analysis of nitrogen-rich polymers
Résumé
The polymeric composition of Titan's tholinsslaboratory analogues of Titan's aerosolssis elucidated using highresolution mass spectrometry. This complex organic matter is produced by plasma discharge in a gaseous nitrogen-methane mixture and analyzed with a hybrid linear trap/orbitrap mass-spectrometer. The highly structured mass spectra are treated with tools developed for petroleomics (Kendrick and van Krevelen diagrams), with original adaptations for nitrogen-rich compounds. Our goal is to find the best chemical basis set to describe the compositional space that these polymers occupy, to shed light onto the chemical structure of tholins. We succeeded in assigning the molecules identified in the mass spectra of tholins to a small number of regularly distributed X-(CH2)m(HCN)n families, where the balanced copolymer (m) n) is determined to play a central role. Within each family, the polymer lengths n and m present Poisson-type distributions. We also identify the smallest species of a subset of families as linear and cyclic amino nitrile compounds of great astrobiological interest: biguanide, guanidin, acetamidine, aminoacetonitrile, and methylimidazole.
Mots clés
aerosols
mass spectra
organic matter
high resolution mass spectrometry
chemistry
basis sets
chemical structure
plasma discharge
amino nitriles
gaseous nitrogen
methylimidazole
polymer length
polymeric compositions
plasma
gas
dielectric barrier discharge
complex organic matters
methane mixtures
nitrogen-rich compounds
elemental composition
haze formation
resonance mass-spectrometry
dissolved organic-matter
titans upper-atmosphere
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