Mechanism Of Gas Phase Molecular Interactions

Among all the halogens that are present in suffient amounts in the stratosphere, bromine radical is the most effective species that participates in efficient catalytic cycles leading to destruction of ozone layer. In spite of the fact that bromine compounds in the stratosphere, it has been estimated that the chemistry involving bromine species is responsible for 25% of the ozone loss obsevered in Antarctica and up to 40% of ozone loss during winter in the Arctic region. The object of this work is the mechanism of BrO with other radicals (ClO,NO2,OH) reaction. The purpose of this work is to study the intermediate geometry configurations and the possible reaction path and provide the help for the experiment. In this dissertation, density functional theory (DFT) has been employed to investigate the reaction mechanism systematically. Firstly, many basis sets of B3LYP of DFT have been used to study BrO radical and other radicals, and tested comparisons of the calculated bond length with the experimental ones show that the DFT-B3LYP/6-31G(3df ) method is more convenient than other basis sets.Subsequently, the DFT-B3LYP method has been used to study the reactions between BrO radical and other radicals. The 6-31G(3df,p) basis set has been employed for hydrogen-containing reactions and the 6-31G(3df ) basis set for other reactions. The following results and conclusions have been reached:1. The reaction mechanism between BrO and ClO. In this work, we report eight conformeric forms of ClOOBr peroxide,and we fistly report three conformeric forms. Among the eight conformeric forms, the most stable is non-conplanar conformeic forms BrOOCl, namely M7. The main reaction pathway is that intermediate M2 decompound to Br radical and OClO, this barrier is 113.27 kJ/mol. Main production is Br radical and OClO.2. The reaction mechanism between BrO and NO2. In this work, we report six conformeric forms of BrONO₂ peroxide. The most stable is conplanar conformeic forms BrONO₂. The main production is Br radical and NO₂, and main reaction pathway is M5â†'M3â†'TS1â†'Br+NO₃. This reaction barrier is 23.26 kJ/mol, which is the most energetically favored pathway.3. The reaction mechanism between BrO and OH. In this work, we present DFT quantum mechanical calculations of both singlet and triplet of the structures. Both singlet and triplet potential energy surfaces predicted by B3LYP/6-31G(3df,p). As for energy, the singlet is more lower than the triplet. The reaction was shown to take place primarily over the singlet surface by two main channels producing HOO+Br. The triplet main channels produing HOO+Br need pass higher barrier which are 22.04 kJ/mol and 17.29 kJ/mol.