Abstrakt

Transition State Study of Ozone Depletion by 1, 2-Dibromo 1, 2-Dichloro Ethane Theoretically

Abbas A-Ali Drea

Ozone depletion by 1, 2-dibromo 1, 2-dichloroethane molecule had been studied theoretically in vacuum using search of transition state by quantum calculation methods (semi empirical, and DFT). Geometry optimized structures, reactivity and chemical stability of bonds have been studied depend on potential energy search of reaction coordinate. Transition state search of quadratic states according RHF have been used to estimate the evolved transition states of photolysis reaction and depletion of ozone. The photolysis reaction occurs at carbon-bromine bond of 1, 2-dibromo1, 2-dichloroethane molecule with 43.183 kCal/mol to give up bromine radical and bromo di-chloro ethyl radical. Second photolysis reaction step included the elimination of second bromine radical to form Trans-dichloro ethylene at 4.773 kCal/mol. The bromine radicals are more responsible for ozone depletion than chlorine radicals because transition states formation of +Br-Cyclic ozone & +Br-Bent ozone are needed lowest energetic values of formation and activation energy of decay oxygen molecules from ozone than other transition state of +Cl-Cyclic ozone & +Cl-Bent ozone. Transition state of +Br-Cyclic ozone is the most probable transition state than the transition state of +Br-Bent ozone as a result of bromine radicals react with cyclic ozone. Transition state of +Br-Cyclic ozone is immediately transformation into the transition state of +Br-Bent ozone with activation energy equal to -10.721 kCal/mol. Each one mole of 1, 2-dibromo1, 2-dichloroethane is depleted two mole of ozone into two mole of oxygen, two mole of BrO compound, and one mole of Transdichloro ethylene.