A Dft Study On The Reaction Between Ch₂=Chx（X=Cl,F）and O₂

Chlorofluorocarbons (CFCs) have tremendous destruction influence on the ozone layer. The existing theory argues that CFCs are dissociated into chloride or fluoride radicals in the ionosphere. These radicals attack ozone, thereby decreasing its concentration. However, for unsaturated CFCs, from the point view of chemical balance, if they can directly react with oxygen molecules to produce atomic oxygen, the process in which ozone decompose into oxygen molecules and oxygen atoms will be inhibited. Thus, the ozone layer is protected. So it is of great significance to study the reaction mechanism between unsaturated CFCs and oxygen molecules. This thesis attempts to research the reaction mechanism between halogenated ethylene, a representative of unsaturated CFCs, and singlet/triplet oxygen molecules to discuss the possibility of producing oxygen atoms. This work will provide important theory basis for inhibiting ozone depletion by chemical methods.In this thesis, using Gaussian software, we investigate the reaction of CH2=CHX(X=Cl, F) with O2at the B3LYP/6-311++G (d, p) level based on density functional theory. The geometry configurations of reactants, products, intermediates and transition states are optimized. All the transition states and reaction pathways are verified by the vibrational analysis and the intrinsic reaction coordinate calculation. We calculate the standard Gibbs free energy change and activation energy for each elementary reaction. And the corresponding zero point correction of the activating energy is given.The main results of the present research are summarized as follows:(1) CH2=CHC1can react spontaneously with triplet oxygen molecules, but not spontaneously with singlet ones. In contrast, CH2=CHF can react spontaneously with singlet oxygen molecules, but not spontaneously with triplet ones.(2) The products of the reaction between CH2=CHCl and triplet oxygen molecules are O (3P), CH3CClO, CO and CH3Cl, CH2CCHO, HCl and CH2=C=O, and H2COCHCl. The most stable ones are CH3CClO and O (3P).(3) The products of the reaction between CH2=CHF and singlet oxygen molecules are O(’P), CH3CFO, HF and CH2=C=O,CO and CH3F, CH2FCHO, and H2COCHF. The most stable ones are CH3CFO and O (1P).(4) CH2=CHX (X=Cl, F) can react spontaneously with oxygen molecules to produce oxygen atoms, thus it can inhibit the ozone dissociation efficiently.