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

Probing the Reaction Dynamics of Hydrogen-Deficient Hydrocarbon Molecules and Radical Intermediates via Crossed Molecular Beams. Ralf I. Kaiser Department of Chemistry University of Hawai’i at Manoa Honolulu, HI 96822 ralfk@hawaii.edu. Introduction. CH x C 2 H x C 3 H x C 4 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. Probing the Reaction Dynamics of Hydrogen-Deficient Hydrocarbon Molecules and Radical Intermediates via Crossed Molecular Beams Ralf I. Kaiser Department of Chemistry University of Hawai’i at Manoa Honolulu, HI 96822 ralfk@hawaii.edu

  2. Introduction CHx C2Hx C3Hx C4Hx C5Hx

  3. Introduction k = 10-11 – 10-12 cm3s-1 T < 1500 K Eact = 5 – 45 kJmol-1

  4. Objectives Investigate the Dynamics and Energetics of Phenyl Radical Reactions

  5. Requirements • Preparation of Highly Reactive Reactant Radicals C6H5(X2A1) C6H5NO  C6H5 + NO ΔT 2. Identify Reaction Products and Infer Reaction Intermediates 3. Obtain Information on Energetics and Reaction Mechanisms ↓ Single Collision Conditions < 0.1 % He seeded 200 Hz; 2800 – 3400 ms-1 Crossed Molecular Beams Experiments

  6. Crossed Molecular Beams Setup Requirements 1. Hydrocarbon Free 2. Extremely Low Pressures Main Chamber = 10-9 torr Detector = 10-11 - < 10-12 torr 3. Signal Maximization

  7. C6H5 + C2H2 26 amu 77 amu

  8. C6H5 + C2D2 28 amu 77 amu

  9. C6H5 + C2H2  C8H6 + H (m/z = 102)

  10. C6H5 + C2H2  C8H6 + H (m/z=102) indirect reaction via intermediate exit barrier Emax = Ec - rG

  11. C6H5 + C2H2  C6H5CCH (m/z = 102) + H X. Gu, F. Zhang, Y. Guo, R.I. Kaiser, Angew. Chemie Int. Edition 46, 6866 (2007).

  12. C6H5 + C2H4  C8H8 + H (m/z=104)

  13. C6H5 + C2D4  C6H5C2D3 + D (m/z=107)

  14. C6H5 + C2H4  C6H5C2H3 + H (m/z=104) indirect via intermediate exit barrier

  15. C6H5 + C2H4  C6H5C2H3 + H (m/z=104) F. Zhang, X. Gu, Y. Guo, R. I. Kaiser, J. Organic Chem. 72, 7597 (2007).

  16. C6H5 + H2CCHCH3 C9H10 + H (m/z=118)

  17. C6H5 + H2CCHCH3 C9H10 + H

  18. C6H5 + C2H3CH3 C9H10 + H F. Zhang, X. Gu, Y. Guo, R.I. Kaiser, JPCA 112, 3284 (2008).

  19. Phenyl Radical Reactions Acetylene Ethylene Methylacetylene Allene Propylene Benzene 80 – 185 kJmol-1

  20. Phenyl Radical Reactions Phenyl versus Hydrogen Exchange Phenyl Group Stays Intact Partially Deuterated Reactants Isomer-Selective Detection Abstraction Reactions < 5 %

  21. Phenyl Radical Reactions Indirect Reaction via Intermediates Exit Barriers for Hydrogen Loss Short Lived Intermediates (no ring closure) Exoergic / Slightly Endoergic

  22. Phenyl Radical Reactions

  23. Phenyl Radical Reactions

  24. Outlook h (266 nm; 248 nm) C6H5NO C6H5 + NO vp = 1800 – 2100 ms-1; EC = 30 – 50 kJmol-1

  25. C2(X1g+/a3u) + C4H6 (1,3-butadiene) C2 + C4H6  C6H5 + H Ec = 13 kJmol-1

  26. C2(X1g+/a3u) + C4H6 (1,3-butadiene) C2 + C4H6  C6H5 + H Ec = 36 kJmol-1

  27. C2 + C4H6  C6H5 + H H2CCDCDCH2 D2CCHCHCD2 phenyl acyclic

  28. C2 + C4H6  C6H5 + H

  29. C2D + C4H6  C6DH5 + H Ec = 45 kJmol-1 H2CCDCDCH2 D2CCHCHCD2

  30. C2D + C4H6  C6DH5 + H 57 ± 10 % 43 ± 10 %

  31. C2D + C4H6  C6DH5 + H relative energy, kJmol-1

  32. Outlook EC = 80 – 185 kJmol-1 EC = 30 - 50 kJmol-1 N  EC = 13 – 45 kJmol-1

  33. Outlook

  34. Outlook

  35. Acknowledgements

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