Ab initio mechanistic and kinetic study of Clx (x=1,2) reactions with HCOOH and HOCO

• Main Authors: Chen, Li-Yang, 陳立揚
• Other Authors: Lin, Ming-Chang
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/nqq429

碩士 === 國立交通大學 === 應用化學系碩博士班 === 103 === The photochemical reactions between chlorine molecules and formic acid are chain reactions which proceed at least partially via chlorofomic acid and the final products detected experementally are carbon dioxide and hydrogen chloride. In order to understand the mechanism of the chain reaction, the Gaussian code was utilized to simulate the reactions of Clx (x=1, 2) with HCOOH and HOCO at the CCSD(T)/aug-cc-pVTZ//BHandHLYP/6-311++G(3df,2p) level of theory. The reactions involved are HCOOH + Cl¬2, HOCO + Cl2, HCOOH + Cl and HOCO + Cl. The HCOOH + Cl2 reaction forms HCOOCl + HCl, with a barrier height of 52.2 kcal mol-1. The rate constant predicted with the transition-state theory is 9.30x10E(-21)T^(2.07)exp(-24404/T) cm3 molecule-1 s-1 in the temperature range from 100 to 2000 K. In the HOCO + Cl2 reaction, HCl + CO2 + Cl are produced via a chlorine atom with a statble complex of chloroformic acid, which fragment with a barrier of 5.3 kcal mol-1. The rate constant predicted with the transition-state theory is 1.73x10E(-17)T^(1.55)exp(893/T) cm3 molecule-1 s-1 in the temperature range from 298 to 2000 K. The hydrogen abstraction from HCOOH by Cl atom is considered as the key process in the chain reaction. In this reaction channel, the barrier height for formation of HOCO + HCl was found to be 2.1 kcal mol-1 and the predicted rate constant is 1.7x10E(-13) cm3 molecule-1 s-1 at 298 K, which is in good agreement with an experimental value of 1.8x10E(-13) cm3 molecule-1 s-1. In the HOCO + Cl reaction, the Cl atom can form a stable complex(ClCOOH) with HOCO, which lies -79.7 kcal mol-1 relative to the reactants; the complex decomposed readily into HCl + CO2 via a transition state with a barrier of 23.4 kcal mol-1. The predicted rate constant is 4.1x10E(-11) cm3 molecule-1 s-1 at 298 K, which is in good agreement with an experimental value of 4.8x10E(-11) cm3 molecule-1 s-1.