Fifth Workshop on Titan Chemistry 11-14 April 2011, Kauai, Hawaii

1. Organic Synthesis In The Atmosphere Of Titan: Modeling and Recent Observations Yuk Yung (Caltech), M. C. Liang (Academia Sinica), X. Zhang (Caltech) Fifth Workshop on Titan Chemistry 11-14 April 2011, Kauai, Hawaii

2. Outline of Today’s Talk Titan: gas phase chemistry Aerosol and surface chemistry

3. Lorenz + Mitton 02

4. [Moses et al., JGR, 2005]

5. tholin CH4 UVIS spectrum Impact: 514 km Liang et al. 2007

6. Photochemical results HCN CH4; hydrostatic HC3N CH4; non-hydrostatic C6N2 C6H6 C6N2; condensation line Liang, Yung, Shemansky ApJ 2007

7. [Lebonnois et al., Icarus, 2001] [Flasar et al., Science, 2005]

8. Photochemical simulation • Two hydrocarbon kinetics tested • Moses et al. (2000) (~80 species + 500 reactions) • Moses et al. (2005) (~100 species + 800 reactions) • Caltech/JPL KINETICS model used • Transport by molecular diffusion alone • Transverse time ~500 sec • Radical lifetime <<1 sec • Stable molecule lifetime >>500 sec • Adjoint model

9. Forward and adjoint models Inverse Model Optimization Improved Estimate Parameter Estimate Gradients (sensitivities) Forward Model Adjoint Model t0 tf tf t0 Predictions Adjoint Forcing - <-- time evolution profiles Observations

10. Lab: Moses et al. (2000) Liang et al. (submitted)

11. Lower atmosphere: Cassini CIRS Liang et al. (submitted)

12. Outline of Today’s Talk Titan: gas phase chemistry Aerosol and surface chemistry

14. Ingredients of Life • Biological Elements • Monomers and polymers in biochemistry • Nucleic acids • Proteins • Lipids and membranes • Carbohydrates • Some other important bio-molecules

15. Precursor to Genetic Material Ribonucleic Acid (RNA) base (adenine, guanine, cytosine, uracil) D-ribose phosphoric acid Polypeptides (proteins) L-aminoacids

16. Study two reactions (Rxns 1 and 2) that considered to be the most • important neutral reactions for benzene and PAH formations on Titan • (from modeling studies by Wilson and Atreya, Yung and Allen, etc.) • 1) C3H3 (propargyl) + C3H3 (+M)  C6H6 (Benzene) • 2) C2H (ethynyl) + C6H6 (benzene) (+M)  PAHs • Gas-phase: investigate the reaction products (and/or intermediates) at • temperature and pressure ranges (200 – 300 K, 0.1 – 20 Torr) relevant to • Titan’s atmospheric conditions. • Matrix-isolation: detect the reaction intermediates (and/or products) in • cryogenic matrices (4 – 100K) to better understand the reaction • mechanisms. Mechanistic Studies of Benzene and PAH Formation on Titan Sander+Zhang

17. Current Results and Significances Energy (kcal/mol) 0 C3H3 + C3H3 Results: At 300-1100ºC and ~300 Torr (average pressure ), the major pyrolysis products are benzene, fulvene and dimethylenecyclobutene. 40 Thermal decomposition of 1,5-hexadiyne in a supersonic pyrolysis nozzle A 80 C D 120 B 160 (B) (D) (A) Significance: Help understand the energetics of the propargyl recombination reaction products and their distributions at different temperature and pressure conditions. (C)

18. I) Polyyne Formation 1) C4H + C2H2→ [C6H3]* → C6H2 (triacetylene) + H Rate constant recently measured; products not detected. 2) C2H + C4H2→ [C6H3]* → C6H2 (triacetylene) + H Rate constant not measured; products detected recently. II) Cyanopolyyne Formation 3) CN + C4H2→ [C5H2N]* → HC5N (cyanodiacetylene) + H Rate constant not measured; products detected recently. Plan to Study Kinetics (Rates and Intermediates/Products) of Polyyne and Cyanopolyyne Formation on Titan

19. The need for elaboration of the large molecule end of the photochemical model of Titan’s atmosphere V.A. Krasnopolsky, 201, 226-256 Icarus (2009). • Lack of specificity in the model • Proposed chemistry highly speculative • Suggests a role for structural isomers Tim Zwier

20. Imanaka et al. (2010), 38th COSPAR meeting N2 (98 %): Catalytic dissociative ionization of CH4 N2 + hv  N2+ + e- N2+ + CH4  N2 + CH3+ + H CH3+ + CH4  C2H5+ + H2 Net) 2CH4 + hv  C2H5+ + H + H2 + e- (Imanaka and Smith, 2007; 2009) EUV generation of unsaturated hydrocarbons, such as benzene N(2D) + N(2D, 4S) + e- N2 N2+ + hn Neutrals/radicals CH2, CH, C + e- + CH4 CH3+ C2H2, C2H3, C2H4, CH3, CH2 + e- + CH4 C2H5+ + C2H2 + C2H4 + C4H2 C3H3+,C3H5+,C4H5+ Ion-molecule reactions

22. Implications - Vis Titan relevant range = Khare et al. (1984) This work • Suggestive that the 2 types of aerosol formation processes result in an observed mixture of 2 types of aerosol with different optical properties. : Hasenkopf et al., Icarus (2010)

23. Acknowledgements We appreciate discussions with Don Shemansky, Michael Line, Run-Lie Shia, and Josh Kammer, and support from NASA Cassini, OPR and PATM.

24. Backup slides

25. Laboratory simulation with synchrotron radiation HCCN heterogeneous chemical growth is plausible in the dusty environment of the Titan upper atmosphere.

27. [Friedson et al., Icarus, 2002]

28. [Moses et al., JGR, 2005]

29. Forward and adjoint models Inverse Model Optimization Improved Estimate Parameter Estimate Gradients (sensitivities) Forward Model Adjoint Model t0 tf tf t0 Predictions Adjoint Forcing - <-- time evolution profiles Observations

30. Comparisons with other studies: (linearly interpolated to λ = 532 nm) Stronger anti-greenhouse effect than Khare. Include more aromatics (benzene  n ~ 1.5) Hasenkopf et al., Icarus (2010)