Mechanism reaction study of ozone with CFC-11 using quantum calculation methods

Abstract EN

-Quantum calculation methods (DFT, Ab-initio, and semiemprical) of the potential energy surface for tropospheric ozone with CFC-11(trichloro, floro-carbon) have been performed which is known to be important in atmospheric chemistry.

Ozone’s forms, reactivity, are optimized at full MP2 level of theory using two basis sets 6-31G*, 6-31G**, also the same thing are carried out for halo carbon Different reaction.

probabilities, suggested structures ,probable transition states for all chemical species related to all possible reaction paths, frontal orbitals ,and wave function calculations, have been optimized and calculate through DFT / B3LYP-RHF-MP2 // 6-31G** and PM3-semimprical configuration interaction.

Vibrational frequencies have been calculated for reactants, products, and transition states up to HF / 6-311G** level of theory.

Twenty three suggested structures and thirty six probably transition states have been studied in this simulation study in gas phase.

The calculation show that, the two forms of Ozone molecules are present and both of them differ in O—O bond stability, its length equal to1.26A⁰ in bent form, and 1.48A⁰ in cyclic form, both of them can be broken with distance equal to 1.99 A⁰ and 1.8 A⁰ respectively.

Halocarbon has two different type of bonds, results indication that’s Cl—C bond is the most probable reactive bond than F—C bond towards photo dissociation reactions.

There are two different suggested pathways for Ozone reaction with halocarbon, its either direct reaction, or indirect reaction through the photolysis of halocarbon bonds .The first pathway is most probable, since Ozone reacted with halocarbon directly O3 + FCCl3------ClO + O2+F*CCl2 with energy barrier equal to 45.51 kcal mol-1, Δ Hreac = -15.541 kcal mol-1.

The most probable second pathway, halocarbon molecule dissociated into two free radicals by UV-light energy FCCl3--------*Cl + F*CCl2 with energy barrier equal to 61.14 kcal mol-1(467.4nm) ,and then free chlorine atoms reacted with Ozone molecules in exothermic reaction *Cl+O3-----ClO + O2 with energy barrier equal to 1.428 kcal mol-1, Δ Hrec = -75.975 kcal mol-1.