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

2. Introduction CH x C 2 H x C 3 H x C 4 H x C 5 H x

3. Objectives Investigate the Formation of Hydrogen-Deficient, Carbon-Bearing Molecules via Reactions of C 2 (X 1  g + /a 3  u ) and C 3 (X 1  g + ) with

4. Requirements 1.Preparation of Highly Reactive Reactants C 2 (X 1  g + /a 3  u ) and C 3 (X 1  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 Main Chamber = 10 -9 torr Detector = 10 -11 - < 10 -12 torr 1. Hydrocarbon Free Requirements Oil Free Pumps (Maglev, Scroll, DryVac) 2. Extremely Low Pressures 3. Signal Maximization Copper Gaskets Cryo Cooling (LN2; Cold Heads) Sources Ionizer, QMS, Ion Counter

6. Crossed Molecular Beams Setup

7. Crossed Beams Experiment

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

9. C 2 (X 1  g + /a 3  u ) + C 2 H 2 (X 1  g + ) TOF at m/z = 49 (C 4 H + ) and m/z = 48 (C 4 + ) superimposableC 4 H Isomer

10. C 2 (X 1  g + /a 3  u ) + C 2 H 2 (X 1  g + ) C 2 (X 1  g + ) + C 2 H 2 (X 1  g + )  C 4 H(X 2  + ) + H( 2 S 1/2 )  R G = - 33.3 kJmol -1 C 2 (a 3  u ) + C 2 H 2 (X 1  g + )  C 4 H(X 2  + ) + H( 2 S 1/2 )  R G = - 41.9 kJmol -1  R G (experimental) = - 40  5 kJmol -1

11. C 2 (X 1  g + /a 3  u ) + C 2 H 2 (X 1  g + ) 33  3 % indirect reaction mechanism(s) via C 4 H 2 complexe(s) 3 – 17 kJmol -1 one channel could have exit barrier

12. C 2 (X 1  g + /a 3  u ) + C 2 H 2 (X 1  g + ) intensity over complete angular rangeindirect reaction dynamics switch from forward to backward peaking as collision energy increases could suggest multiple reaction channels

13. productsreaction enthalpy, kJmol -1 C 4 H(X 2  + ) + H( 2 S 1/2 ) - 33 c-C 3 H 2 (X 1 A 1 ) + C( 3 P j )+ 152 C 4 (X 3  u ) + H 2 (X 1  g + ) -10 c-C 3 H(X 2 B 1 ) + CH(X 2   ) + 246 CH 2 (X 3 B 1 ) + C 3 (X 1  g + ) + 142 C 2 H(X 2  + ) + C 2 H(X 2  + ) + 68 C 2 (X 1  g + /a 3  u ) + C 2 H 2 (X 1  g + )

14. C 2 (X 1  g + ) + C 2 H 2 (X 1  g + ) forward-backward symmetric center-of-mass angular distributions

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

16. Remaining Questions symmetry or long-lived can heavy isotopes induce ISC? C 2 D 2 (X 1  g + ) 13 C 2 H 2 (X 1  g + ) C 2 HD(X 1  + )

17. C 2 (X 1  g + /a 3  u ) + C 2 D 2 (X 1  g + )/ 13 C 2 H 2 (X 1  g + )/C 2 HD(X 1  + ) solely atomic hydrogen/deuterium loss pathwaysno induced ISC

18. C 2 (X 1  g + /a 3  u ) + C 2 D 2 (X 1  g + )/ 13 C 2 H 2 (X 1  g + )/C 2 HD(X 1  + ) E c = 29 kJmol -1 identical CM functions compared to non-labeled reactant long lived diacetylene intermediate no induced ISC HD 13

19. Summary C 2 (X 1  g + /a 3  u ) Reactions 1.identification of dicarbon vs. atomic hydrogen exchange pathway + CH 3 C 6 H 6 PES + C 5 H 5 JCP 113, 9622 (2000) JCP 113, 9637 (2000) JCP 115, 5107 (2001) C 10 H 8 PES

20. Summary C 2 (X 1  g + /a 3  u ) Reactions 2. i ndirect reaction dynamics via barrier less 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 C 2 (X 1  g + /a 3  u ) Reactions

22. 1.identification of tricarbon versus atomic/molecular hydrogen exchange Summary C 3 (X 1  g + ) Reactions + CH 3 C 6 H 6 PES + C 4 H 5 C 10 H 8 PES

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

24. Summary C 3 (X 1  g + ) Reactions

25. Summary 3. identification of building blocks and precursors to PAHs in combustion flames 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 C 4 H x (x = 1 -4) C 5 H x (x = 1 - 4) C 6 H x (x = 3, 4) C 6 H 6 PES C 10 H 8 PES

26. Summary

27. Outlook I C4Hx 1234 C5Hx 1234 C6Hx 34 C4Hx 1234 C5Hx 1234 C6Hx 34 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) experiments suggest inclusion of distinct isomers and additional molecules

28. Outlook II soft electron impact ionization 1. Brink type ionizer made of Alloy 718 (Nickel Alloy w/o H 2 & CO outgassing; strongly reduced CO 2 background) 2. Thoriated Iridium vs LaB 6 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)