Photolysis Dynamics Laser Chemistry Lab

Citation:

Hsu, M-Y, Tsai P-Y, Wei Z-R, Chao M-H, Zhang B, Kasai T, Lin K-C.  2013.  Competitive bond rupture in the photodissociation of bromoacetyl chloride and 2- and 3-bromopropionyl chloride: Adiabatic versus diabatic dissociation. ChemPhysChem. 14:936-945., Number 5

Abstract:

Competitive bond dissociation mechanisms for bromoacetyl chloride and 2- and 3-bromopropionyl chloride following the 1[n(O) →π*(Cï£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 Cï£O chromophore. C-Cl bond fission is anticipated to follow an adiabatic potential surface for a strong diabatic coupling between the n(O)π*(Cï£O) and np(Cl)σ*(C-Cl) bands. In contrast, C-Br bond fission is subject to much weaker coupling between n(O)π*(Cï£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. Busted open: Insight into the mechanisms causing C-Cl and C-Br bond fission of bromoacetyl chloride and 2- and 3-bromopropionyl chloride by following the 1[n(O) →π*(Cï£O)] transition is obtained. The figure shows the center-of-mass translational energy distributions of ground-state Br formation through a diabatic pathway for the dissociation of 2-bromopropionyl chloride. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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