Theoretical Study and Rate constant calculation of the Cl +O
3and ClO + Hg Reaction
Farhad Taheri, Morteza Vahedpour
Chemistry Department, Zanjan University, Zanjan, Iran
Introduction:
Ozone depletion in the polar stratosphere has become a global environmental problem.
The importance of Chlorine and Bromine in the Earth atmosphere particularly in reaction that lead to the loss of ozone is now widely recognized. Both bromine and chlorine react with ozone in the form of below.
X + O3 → XO + O2 XO + O → X + O2
(R1)
(R2)
Where X is Cl and Br.
Although bromine is less abundant than chlorine, it has greater potential to destroy stratospheric ozone. Kinetic of the reaction between ClO and mercury also study and the rate constant of this reaction calculated too.
XO + Hg → HgXO (R3)
Computational Method
All geometries (reactant, product, complexes and transition state (TS)) were fully optimized at the HF level with the 6-31G(d) basis set for oxygen and chlorine atoms and LANL2DZ using the G98 program.. Transition state structures obtained from QST2 with converting reactant to product. Additionally, intrinsic reaction coordinate calculation (IRC) was performed to examine the correspondence of the calculated TS to the reactants and products. Rate constants and frequency factors have been obtained utilizing transition state theory(TST).
Results and Discussion
According to the following reaction possible mechanisms for reaction of chlorine atom and ozone in gas phase involve two intermediates (IM1, IM2) and transition state (TS1).
Cl + O3 → IM1
→ TS1 → IM2 →
ClO
+ O 2
The impact of Hg and ClO produce intermediate (IM3) which convert to the HgClO via TS2 according the following reaction.
Hg + ClO → IM3 → TS2 → HgClO
Optimized geometry of TS1, TS2, IM1, IM2 and IM3 are shown in figure 1.
IM1 TS1 IM2
IM3 TS2
HgClO
Figure 1. Optimized geometry of TS1, TS2, IM1, IM2, IM3, HgClO.
Transition states confirm via IRC test. IRC diagrams are represented in figure
250
1 3
I
R1 R3
Figure II.IRC diagram for R1 and R3 TS conforming.
Rate constant calculation: Finally rate constants for both reactions were calculated which equal to: k = 5.2911×10−8 k = 7.8026 ×10−17
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