Abstract Submissions

Titan’s Tholins: How can we determine the components of organic “Paradise”? An FT-ICR study.

Árpád Somogyi¹, Véronique Vuitton², Roland Thissen²

¹Mass Spectrometry and Proteomics Facility, Chemistry Campus Instrumental Center, The Ohio State University, Columbus, OH, ²Institut de Planétologie et d’Astrophysique de Grenoble, Grenoble, France
Saturn’s largest moon, Titan, is often described as an “organic paradise”; its atmosphere resembles the early (reductive) atmosphere of Earth. The great success of the Cassini-Huygens mission allowed direct detection of ions and neutrals in Titan’s atmosphere by using the ion-neutral mass spectrometer (INMS) mounted on the Cassini spacecraft. Unfortunately, the “in situ” measurements on Titan have limitations due to limited mass resolution or mass range. Using model reactions and ultrahigh resolution mass spectrometers here on Earth are, currently, the only way to obtain detailed and comprehensive information on ion-molecule processes and their products. Tholins are organic polymers which have a general formula of CxHyNz. More saturated compounds (imines, amines) are detected in the positive mode, while more unsaturated compounds indicate compounds rich in CN group contribution. These differences can be easily visualized on van Krevelen plots. Many of the CxHyNz polymers can be hydrolyzed with water and/or ammonia/ice water that leads to CxHyNzOn molecules. Hydrolysis kinetics measured from Arrhenius activation energies have been determined indicating that oxygen incorporation can occur in a 3,000-10,000-year time frame even at around 100 K (surface temperature). Our recent study showed that, overall, both ESI and LDI resulted in complex negative ion MS spectra that contains several hundreds of ions in the m/z range of 50-300. LDI produced more CxNz- ions, such as C10N5-, which we assigned as the pentacyanide cyclopentadiene ion that was supported by MS/MS measurements (CID, QCID, SORI, and IRMPD). To our best knowledge this is the first time when the characteristic νCN stretching vibration band was detected for a deprotonated tetracyanide. Quantum chemical calculations predict the formation of small anionneutral complexes that can be considered as “seeds” for larger covalent and/or non-covalent complexes.