| The very important environmental problem to human is the spectacular loss of stratospheric ozone. Many chemical matters cause the ozone losses. The reactions involved with ozone are almost related to the radical and small active molecule. At present, people have recognized that the main contributors to ozone depletion in the stratosphere is radicals such as ClOx, BrOx and HOx and compounds of NOx. Previous literature has obtained temperature-controled rate constants in the experiment,employing spectrum technique and confirmed the products and the main reaction path. However, to our knowledge, there have been no attempts to model in detail the reaction mechanism, and few theoretical studies about them. In this letter, we use B3LYP and HF method provided by Gaussian98 program package with 6-31G(d) basis set to investigate the reaction of ClONO2 with the radicals (Cl,H,O )and HCl ,trying to make sure the main reaction paths. There are three reaction paths in the reaction of ClONO2 and Cl atom as follows:ClONO2+Clâ†'Cl2+NO3 (1)ClONO2+Clâ†'ClOCl+NO2 (2)ClONO2+Clâ†'ClO+ClONO (cis) (3)The first and the third reaction are the exothermic reactions, and the reaction energies are 65.595KJ/Mol and 25.961KJ/Mol.The second one is the endothermic reaction, the reaction energy is 21.511KJ/Mol.The first reaction mechanism is that atom Cl attacks the Cl of nitrate, meanwhile, the Cl-O bond breaks, and the products formed. As for the second reaction, atom Cl attacks atom O bonded by Cl in nitrate, and the bond N-O breaks to create the products. The third is to attack terminal atom O of the radical and the bond breaks. The results show that the reaction activation energy of the first reaction is 4.445KJ/Mol; the activation energies of the second and the third reaction are 37.266KJ/Mol and 57.607KJ/Mol respectively. It's obvious that the first reaction is therefore the main reaction because of its low activation energy. And the third reaction is far more difficult than the former two reactions.The possible reaction between chlorine nitrate and hydrogen are as follows: H+ ClONO2â†'Cl+HONO2 (1)H+ ClONO2â†'OH+ClONO(cis) (2)H+ ClONO2â†'OH+ClONO(trans) (3)The above three reactions are all exothermic reactions. The first reaction energy is 247.782KJ/Mol, the second reaction energy is 133.625KJ/Mol, and the third is 111.374KJ/Mol. The three activation energies are almost the same and respectively are 19.549KJ/Mol, 20.001KJ/Mol and 23.228KJ/Mol. In the dynamic way, comparing the activation energy, we conclude that the three reactions can occur with the same possibility. The first reaction gives so more energy than the others that it is more likely to occur.The possible reaction between chlorine nitrate and oxygen as follows:O(3P)+ClONO2â†'ClO+NO3 (1) O(3P)+ClONO2â†'O2+ClONO (2)The activation energies of the two reactions are 1.05KJ/Mol and 88.416KJ/Mol.So the first reaction is the main reaction path.The reaction between chlorine nitrate and hydrogen chloride as follows:HCl+ClONO2â†'Cl2+HONO2The aforementioned reaction has two distinct reaction channels leading to the same products including chlorine and nitric acid.One channel is that H of HCl attacks the Cl-bonded O element with the transion state having out-of -plane position. But another reaction channel take a psudo-plane approach way with H of HCl attacking the terminal oxygen ,The reaction energy is 47.503KJ/Mol.The two channels activation energies are 164.879 KJ/Mol and 0.7 KJ/Mol.respectively So unambiguously second reaction is the main reaction path. |
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