Unimolecular Reaction Theoretical Studies And Construction Of Potential Energy Surface

This dissertation is composed of two parts. The first part is the detailed studies of unimolecular dissociation reactions by ab initio/RRKM theory ; the second part is the construction of six-dimensional PES for four-atom photodissociation reaction by interpolated method.The first reaction system studied by ab initio/RRKM is O(¹D) + NH₃ collision reaction, which is shown to occur mainly through the insertion mechanism involving the long-lived chemically activated NH₂OH* intermediate. This energized intermediate quickly dissociates to various products via some critical configurations. The calculated branching ratios of various decomposition products of NH2OH* are in good agreement with recently reported experimental values. This reaction can also proceed through the addition/abstraction mechanism on the first excited-state PES, which partially accounts for the forward scattering of the OH products observed in experiment.The CH₃F intermediate can be formed without a barrier by F + CH₃ collision , then dissociate via four product channels, including F + CH₃, HF + CH₂, H₂ + CHF, and H + CH₂F. RRKM theory is applied to compute rate constants and branching ratios of the four product channels at various collision energies and temperatures. H + CH₂F are predicted to be the major reaction products (except at low temperatures) followed by H₂ + CHF. The H abstraction mechanism leading to HF + CH₂ over a low barrier, 1.4kcal/mol, is also important at high collision...