Comparison of soluble and insoluble organic matter in analogues of Titan's aerosols

Maillard, Julien; Carrasco, Nathalie; Schmitz-Afonso, Isabelle; Gautier, Thomas; Afonso, Carlos

doi:10.1016/j.epsl.2018.05.014

Cited by 45 publications

(63 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The presence of the C 1 (at m/z 15 and 18) and C 2 (at m/z 28 and 29) ions in this condition (CH 3 + /NH 4 + and HCNH + /C 2 H 5 + , respectively) is significant. This comes in agreement with the copolymeric HCN/C 2 H 4 and poly-(CH 2 ) m (HCN) n -based structure found in the solid tholin material (Pernot et al, 2010;Gautier et al, 2014;Maillard et al, 2018). As the tholins are negatively charged, they may react with these major ions to nucleate and polymerize.…”

Section: Group M/zsupporting

confidence: 87%

Positive ion chemistry in an N2-CH4 plasma discharge: Key precursors to the growth of Titan tholins

Dubois

Carrasco

Jovanović

et al. 2020

Icarus

Self Cite

View full text Add to dashboard Cite

Titan is unique in the solar system as it hosts a dense atmosphere mainly made of molecular nitrogen N 2 and methane CH 4 . The Cassini-Huygens Mission revealed the presence of an intense atmospheric photochemistry initiated by the photo-dissociation and ionization of N 2 and CH 4 . In the upper atmosphere, Cassini detected signatures compatible with the presence of heavily charged molecules which are precursors for the solid core of the aerosols. These observations have indicated that ion chemistry has an important role for organic growth. However, the processes coupling ion chemistry and aerosol formation and growth are still mostly unknown. In this study, we investigated the cation chemistry responsible for an efficient organic growth that we observe in Titan's upper atmosphere, simulated using the PAMPRE plasma reactor. Positive ion precursors were measured by in situ ion mass spectrometry in a cold plasma and compared with INMS observations taken during the T40 flyby. A series of positive ion measurements were performed in three CH 4 mixing ratios (1%, 5% and 10%) showing a variability in ion population. Low methane concentrations result in an abundance of amine cations such as NH 4 + whereas aliphatic compounds dominate at higher methane concentrations. In conditions of favored tholin production, the presence of C 2 compounds such as HCNH + and C 2 H 5 + is found to be consistent with copolymeric growth structures seen in tholin material. The observed abundance of these two ions particularly in conditions with lower CH 4 amounts is consistent with modeling work simulating aerosol growth in Titan's ionosphere, which includes mass exchange primarily between HCNH + and C 2 H 5 + and negatively charged particles. These results also confirm the prevalent role of C 2 cations as precursors to molecular growth and subsequent mass transfer to the charged aerosol particles as the CH 4 abundance decreases towards lower altitudes.

show abstract

Section: Group M/zsupporting

confidence: 87%

Positive ion chemistry in an N2-CH4 plasma discharge: Key precursors to the growth of Titan tholins

Dubois

Carrasco

Jovanović

et al. 2020

Icarus

Self Cite

View full text Add to dashboard Cite

show abstract

“…Noticeably, neither series agree very well with the observed pattern and moreover an overall slightly flattening of the pattern (decrease of the slope) at higher m/z is revealed. Based on previous molecular level studies on tholins [5,7,9], we hypothesize ramified archipelago-type nitrogen-containing PAHs (N-PAHs) as the primary structural element ( Figure S1). Theoretical calculations of the cross-sections for those species, given as blue line in Figure 1, revealed an excellent agreement to the experimentally observed data.…”

Section: Resultsmentioning

confidence: 92%

Structural Study of Analogues of Titan’s Haze by Trapped Ion Mobility Coupled with a Fourier Transform Ion Cyclotron Mass Spectrometer

Rueger

Maillard

Maitre

et al. 2019

J. Am. Soc. Mass Spectrom.

Self Cite

View full text Add to dashboard Cite

The aerosols present in the atmosphere of the Saturn's moon Titan are of particular planetary science interest and several spacecraft missions already allowed to gather spectroscopic data. Titan haze's analogs, so-called tholins, were produced on earth to push forward the comprehension of their formation and properties. In this study, this highly complex mixture was analyzed here for the first time by trapped ion mobility spectrometry coupled to ultra-high resolution mass spectrometry (FTICR MS). Electrospray ionization revealed the characteristic CHN x -class components, with CHN 5-6 and DBE 6-7 most abundant. Deploying specialized visualization, enabled by accurate mass measurements and elemental composition assignments, the adapted Kendrick mass defect analysis highlights the C 2 H 3 N homolog series, whereas the nitrogen-modified van Krevelen diagram exhibits a clear trend towards H/C 1.5 and N/C 0.5. More interestingly, the representation of m/z versus collision cross section (CCS) allowed hypothesizing a ramified N-PAH structural motif. State-of-the-art IMS is currently not able to resolve the isomeric continuum of ultra-complex mixtures; thus peak parameter other than the CCS-value are explored. As such, analyzing the mobility peak width versus m/z shows a linear increase in isomeric diversity between m/z 170 and 350 and a near plateau in diversity at higher m/z for the N-PAH-like structure. Due to the high complexity of the sample, these structural insights are only to be revealed by TIMS-FTICR MS.

show abstract

“…Analyses of laboratory analogues of these aerosols show polymeric structures and various functional groups such as nitrile, amine, aliphatic and aromatic hydrocarbons (e.g. Morrison et al 2016, Sciamma-O'Brien et al 2017, Maillard et al 2018. This material should be essentially diamagnetic but it likely contains a small fraction of magnetic sites.…”

Section: Magnetic Interaction On Aerosol Surfacementioning

confidence: 99%

On the H2 abundance and ortho-to-para ratio in Titan's troposphere

Bézard

Vinatier

2020

Icarus

View full text Add to dashboard Cite

We have analyzed spectra recorded between 50 and 650 cm -1 by the Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft at low and high emission angles to determine simultaneously the H2 mole fraction and ortho-to-para ratio in Titan's troposphere.We used constraints from limb spectra between 50 and 900 cm -1 and from in situ measurements by the Huygens probe to characterize the temperature, haze and gaseous absorber profiles. We confirm that the N2-CH4 collision-induced absorption (CIA) coefficients used up to now need to be increased by about 52% at temperatures of 70-85 K.We find that the N2-N2 CIA coefficients are also too low in the N2 band far wing, beyond 110 cm -1 , in agreement with recent quantum mechanical calculations. We derived a H2 mole fraction equal to (0.88 ± 0.13) × 10 -3 , which pertains to the ~1-34 km altitude range probed by the S0(0) and S0(1) lines. This result agrees with a previous determination based only on the H2-N2 dimer transition in the S0(0) line, and with the in situ measurement by the Gas Chromatograph Mass Spectrometer (GCMS) aboard Huygens. It is 3-4 times smaller than the value measured in situ by the Ion Neutral Mass Spectrometer (INMS) of Cassini at 1000-1100 km. The H2 para fraction is close to equilibrium in the 20-km region. CIRS spectra can be fitted assuming ortho-to-para (o-p) H2 thermodynamical equilibrium at all levels or a constant para fraction in the range 0.49-0.53. We have investigated different mechanisms that may operate in Titan's atmosphere to equilibrate the H2 o-p ratio and we have developed a onedimensional model that solves the continuity equation in presence of such conversion mechanisms. We conclude that exchange with H atoms in the gas phase or magnetic interaction of H2 in a physisorbed state on the surface of aerosols are too slow compared with atmospheric mixing to play a significant role. On the other hand, magnetic interaction of H2 with CH4, and to a lesser extent N2, can operate on a timescale similar to the vertical mixing time in the troposphere. This process is thus likely responsible for the o-p equilibration of H2 in the mid-troposphere implied by CIRS measurements. The model can reproduce the inferred o-p ratio in the 20-km region, assuming low atmospheric mixing in the troposphere down to 15-20 km and conversion rates with CH4 or N2 slightly larger than obtained from an extrapolation of natural ortho-para conversion rate measured in gaseous hydrogen.

show abstract

Comparison of soluble and insoluble organic matter in analogues of Titan's aerosols

Cited by 45 publications

References 46 publications

Positive ion chemistry in an N2-CH4 plasma discharge: Key precursors to the growth of Titan tholins

Positive ion chemistry in an N2-CH4 plasma discharge: Key precursors to the growth of Titan tholins

Structural Study of Analogues of Titan’s Haze by Trapped Ion Mobility Coupled with a Fourier Transform Ion Cyclotron Mass Spectrometer

On the H2 abundance and ortho-to-para ratio in Titan's troposphere

Contact Info

Product

Resources

About