Energetic Diagrams and Structural Properties of Monohaloacetylenes HC CX (X = F, Cl, Br)

Abstract : Highly correlated electronic wavefunctions within the Multi Reference Con gura- tion Interaction (MRCI) approach are used to study the stability and the formation processes of the monohaloacetylenes HCCX and monohalovinylidenes C2HX (X = F, Cl, Br) in their electronic ground state. These tetra-atomics can be formed through the reaction of triatomic fragments C2F, C2Cl, C2Br with an hydrogen atom or of C2H with halogen atoms via barrierless reactions whereas the reactions between the diatomics [C2 + HX] need to overcome barriers of 1.70 eV, 0.89 eV and 0.58 eV for X = F, Cl, Br. It is found that the linear HCCX isomers, in singlet symmetry, are more stable than the singlet C2HX iso-forms by 1.995 eV, 2.083 eV and 1.958 eV for X = F, Cl, Br. The very small isomerization barriers from iso to linear forms are calculated 0.067 eV, 0.044 eV and 0.100 eV for F, Cl and Br systems. The dissociation energies of the HCCX systems (without ZPE corrections), resulting from the breaking of the CX bond, are calculated to be 5.647 eV, 4.691 eV and 4.129 eV for X = F, Cl, Br respec- tively. At the equilibrium geometry of the X1+ state of HCCX, the vertical excitation energies in singlet and triplet symmetries are all larger than the respective dissociation energies. Stable excited states are found only as 3A′, 3A′′ and 1A′′ monohalovinylidene structures.
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Submitted on : Tuesday, September 19, 2017 - 2:38:12 PM
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Khiri Dorra, Majdi Hochlaf, Gilberte Chambaud. Energetic Diagrams and Structural Properties of Monohaloacetylenes HC CX (X = F, Cl, Br) . Journal of Physical Chemistry A, American Chemical Society, 2016, 120 (30), pp.5985. ⟨hal-01590337⟩

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