title: Competitive bond rupture in the photodissociation of bromoacetyl chloride and 2- and 3-bromopropionyl chloride: adiabatic versus diabatic dissociation.
abstract: Competitive bond dissociation mechanisms for bromoacetyl chloride and 2- and 3-bromopropionyl chloride following the (1) [n(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.
authors: Department of Chemistry, National Taiwan University, Taipei 106, Taiwan.
authors: Ming-Yi
authors: MY
authors: Hsu
authors: Po-Yu
authors: PY
authors: Tsai
authors: Zheng-Rong
authors: ZR
authors: Wei
authors: Meng-Hsuan
authors: MH
authors: Chao
authors: Bing
authors: B
authors: Zhang
authors: Toshio
authors: T
authors: Kasai
authors: King-Chuen
authors: KC
authors: Lin