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Ralf I. Kaiser Department of Chemistry University of Hawai’i at Manoa Honolulu, HI 96822

Investigating the Chemical Dynamics of Bimolecular Reactions of Dicarbon and Tricarbon Molecules with Unsaturated Hydrocarbons. Ralf I. Kaiser Department of Chemistry University of Hawai’i at Manoa Honolulu, HI 96822 kaiser@gold.chem.hawaii.edu. Introduction. CH x C 2 H x C 3 H x

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Ralf I. Kaiser Department of Chemistry University of Hawai’i at Manoa Honolulu, HI 96822

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  1. Investigating the Chemical Dynamics of Bimolecular Reactions of Dicarbon and Tricarbon Molecules with Unsaturated Hydrocarbons Ralf I. Kaiser Department of Chemistry University of Hawai’i at Manoa Honolulu, HI 96822 kaiser@gold.chem.hawaii.edu

  2. Introduction CHx C2Hx C3Hx C4Hx C5Hx

  3. Objectives Investigate the Formation of Hydrogen-Deficient, Carbon-Bearing Molecules via Reactions of C2(X1g+/a3u) and C3(X1g+) with

  4. Requirements • Preparation of Highly Reactive Reactants • C2(X1g+/a3u) and C3(X1g+) 2. Identify Reaction Products and Infer Reaction Intermediates 3. Obtain Information on Energetics and Reaction Mechanisms ↓ Single Collision Conditions Crossed Molecular Beams Experiments

  5. Crossed Molecular Beams Setup Requirements 1. Hydrocarbon Free Oil Free Pumps (Maglev, Scroll, DryVac) 2. Extremely Low Pressures Copper Gaskets Cryo Cooling (LN2; Cold Heads) Main Chamber = 10-9 torr Detector = 10-11 - < 10-12 torr 3. Signal Maximization Sources Ionizer, QMS, Ion Counter

  6. Crossed Molecular Beams Setup

  7. Crossed Beams Experiment

  8. Crossed Molecular Beams Experiments 10 – 50 kJmol-1 peak collision energy 72 - 175 kJmol-1 20 collision energies 14 9 labeling experiments 5 3,000 – 3,800 K 1,500 – 2,600 K

  9. C2(X1g+/a3u) + C2H2(X1g+) TOF at m/z = 49 (C4H+) and m/z = 48 (C4+) superimposable C4H Isomer

  10. C2(X1g+/a3u) + C2H2(X1g+) C2(X1g+) + C2H2(X1g+)  C4H(X2+) + H(2S1/2) RG = - 33.3 kJmol-1 C2(a3u) + C2H2(X1g+)  C4H(X2+) + H(2S1/2) RG = - 41.9 kJmol-1 RG(experimental) = - 40  5 kJmol-1

  11. C2(X1g+/a3u) + C2H2(X1g+) indirect reaction mechanism(s) via C4H2 complexe(s) 33  3 % one channel could have exit barrier 3 – 17 kJmol-1

  12. C2(X1g+/a3u) + C2H2(X1g+) intensity over complete angular range indirect reaction dynamics switch from forward to backward peaking as collision energy increases could suggest multiple reaction channels

  13. C2(X1g+/a3u) + C2H2(X1g+)

  14. C2(X1g+) + C2H2(X1g+) forward-backward symmetric center-of-mass angular distributions

  15. C2(X1g+/a3u) + C2H2(X1g+) 1. exit barrier 2. shallow potential energy wells - asymmetric center-of-mass angular distributions 3. switch from forward to backward - impact parameter dependence ?

  16. Remaining Questions can heavy isotopes induce ISC? C2D2(X1g+) 13C2H2(X1g+) C2HD(X1+) symmetry or long-lived

  17. C2(X1g+/a3u) + C2D2(X1g+)/13C2H2(X1g+)/C2HD(X1+) solely atomic hydrogen/deuterium loss pathways no induced ISC

  18. C2(X1g+/a3u) + C2D2(X1g+)/13C2H2(X1g+)/C2HD(X1+) Ec = 29 kJmol-1 no induced ISC long lived diacetylene intermediate identical CM functions compared to non-labeled reactant H D 13 13

  19. Summary C2(X1g+/a3u) Reactions • identification of dicarbon vs. atomic hydrogen exchange pathway JCP 113, 9622 (2000) JCP 113, 9637 (2000) JCP 115, 5107 (2001) + CH3 + C5H5 C10H8 PES C6H6 PES

  20. Summary C2(X1g+/a3u) Reactions 2. indirect reaction dynamics via barrierless addition of dicarbon to the -bond of the hydrocarbon yielding initially acyclic/cyclic collision complexes 3. reactions are exoergic 4. assignment of intermediates

  21. Summary C2(X1g+/a3u) Reactions

  22. Summary C3(X1g+) Reactions • identification of tricarbon versus atomic/molecular hydrogen exchange + CH3 + C4H5 C10H8 PES C6H6 PES

  23. Summary C3(X1g+) Reactions 2. reactions have pronounced entrance barriers molecule entrance barrier Eo, kJmol-1 acetylene 95  20 ethylene 42  4 methylacetylene 42  6 allene 42  6 benzene in progress (E) ~ [1- Eo/E] 3. borderline of direct/indirect reaction dynamics via addition of tricarbon to the -bond of the hydrocarbon 4. reactions are endo (acetylene) / exoergic 5. assignment of intermediates

  24. Summary C3(X1g+) Reactions

  25. Summary 1.conducted crossed beams experiments of dicarbon and tricarbon with small unsaturated hydrocarbons (10 – 175 kJmol-1) 2.inferred reaction dynamics and energetics of the reactions 3.identification of building blocks and precursors to PAHs in combustion flames C4Hx (x = 1 -4) C5Hx (x = 1 - 4) C6Hx (x = 3, 4) C6H6 PES C10H8 PES

  26. Summary

  27. Outlook I A Mechanism of Aromatics Formation and Growth in Laminar Premixed Acetylene and Ethylene Flames http://www.me.berkeley.edu/soot/mechanisms/mechanisms.html (Michael Frenklach) C4Hx 1 2 3 4 C5Hx1 2 34 C6Hx 3 4 experiments suggest inclusion of distinct isomers and additional molecules

  28. Outlook II softelectron impact ionization 1. Brink type ionizer made of Alloy 718 (Nickel Alloy w/o H2 & CO outgassing; strongly reduced CO2 background) 2. Thoriated Iridium vs LaB6 Filament (1,600 K vs. 1,200 K ) 0.9 mA @ 8 eV

  29. Acknowledgements Xibin Gu, Ying Guo, Fangtong Zhang (UH) Alexander M. Mebel (FIU)

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