Competitive Bond Rupture in the Photodissociation of Bromoacetyl Chloride and 2‐ and 3‐Bromopropionyl Chloride: Adiabatic versus Diabatic Dissociation |
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Authors: | Ming‐Yi Hsu Dr Po‐Yu Tsai Zheng‐Rong Wei Meng‐Hsuan Chao Prof Bing Zhang Prof Toshio Kasai Prof King‐Chuen Lin |
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Institution: | 1. Department of Chemistry, National Taiwan University, Taipei 106 (Taiwan);2. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106 (Taiwan);3. State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (People's Republic of China);4. Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560‐0043 (Japan) |
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Abstract: | Competitive bond dissociation mechanisms for bromoacetyl chloride and 2‐ and 3‐bromopropionyl chloride following the 1n(O)→π*(C?O)] transition at 234–235 nm are investigated. Branching ratios for C? Br/C? Cl bond fission are found by using the (2+1) resonance‐enhanced multiphoton ionization (REMPI) technique coupled with velocity ion imaging. The fragment branching ratios depend mainly on the dissociation pathways and the distances between the orbitals of Br and the C?O chromophore. C? Cl bond fission is anticipated to follow an adiabatic potential surface for a strong diabatic coupling between the n(O)π*(C?O) and np(Cl)σ*(C? Cl) bands. In contrast, C? Br bond fission is subject to much weaker coupling between n(O)π*(C?O) and np(Br)σ*(C? Br). Thus, a diabatic pathway is preferred for bromoacetyl chloride and 2‐bromopropionyl chloride, which leads to excited‐state products. For 3‐bromopropionyl chloride, the available energy is not high enough to reach the excited‐state products such that C? Br bond fission must proceed through an adiabatic pathway with severe suppression by nonadiabatic coupling. The fragment translational energies and anisotropy parameters for the three molecules are also analyzed and appropriately interpreted. |
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Keywords: | cleavage reactions bond energy reaction mechanisms diabatic effects velocity ion imaging |
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