Quantum Chemical And Molecular Dynamics Simulations Of The Acid-base Catalyzed Hydrolysis Mechanism Of Carbonyl Fluoride (CF₂O)

Carbonyl fluoride(CF2O),as one of the degradation products of hydrocarbon compounds containing fluorine,is important inorganic fluorine in the atmospheric environment.Because of the high stability of CF2O molecules,their atmospheric concentration increases year by year,accounting for one-third of the inorganic fluoride in the atmosphere.In recent years,the hydrolysis reaction of CF2O has been considered as one of the main pathways to remove CF2O from the atmosphere.Based on the preliminary experimental observations and some theoretical studies,it was systematically studied that the hydrolysis of CF2O and its catalytic hydrolysis reaction by using quantum chemistry calculation and ab initio molecular dynamics simulation in this paper.This paper contains five chapters,which are:Chapter 1 summarizes the research status of experimental observation and theoretical calculation of CF2O in the atmosphere,and determines the necessity of studying the water reaction of CF2O;Chapter 2 introduces the principle of quantum chemistry calculation and ab initio molecular dynamics simulation method.In Chapter 3 and 4,the hydrolysis and catalytic hydrolysis mechanism of CF2O are discussed in detail employing quantum chemical calculation and ab initio molecular dynamics simulation respectively.Chapter 5 is the summary and prospect of this research.To sum up,the main content in this paper includes two parts:Part 1,the CF2O hydrolysis reaction and its H2O,base(NH3 and CH3NHCH3)and acid(HCOOH,CF3COOH and H2SO4)catalytic hydrolysis mechanism on the atmospheric environment were investigated at the CCSD(T)/aug-cc-pvTZ//M06-2X/6-311++G(3df,3pd)level.The results show that the CF2O hydrolysis reaction contains four elementary reactions:addition,elimination,substitution and decomposition and its addition-elimination route is a lower energy route.For the addition reaction,all catalytic molecules significantly decrease the reaction of barrier height by 20.4-28.8 kcal·mol-1.Here two H-transfer mechanisms have been identified in these catalyzed hydrolytic reactions as asynchronous collaborative caused by base molecules and the synchronous collaborative led by H2O and acid molecules.In addition,the rate coefficient and relative rate of all catalytic reactions have calculated using conventional transition state theory(TST)over a temperature range of 280-320 K.The results show that H2SO4 has the best catalytic effect without considering the concentration of catalyst molecules in the atmosphere.On the contrary,a high concentration of HCOOH(10 ppbv)is dominant in the catalytic reaction when considered the concentrations of catalyst molecules.Part 2,was studied by ab initio molecular dynamics(BOMD)that the hydrolysis reaction of CF2O and its acid-base catalytic hydrolysis reaction at 300 K.In BOMD simulation,the hydrolytic reaction of CF2O without any catalyst or within H2O,base(NH3)and acid(H2SO4)respectively have not been observed within 10 ps,indicating that the time scale of reaction was far beyond 10 ps.However,the addition-reaction and elimination-reaction for the hydrolytic reaction of CF2O were respectively observed at only 1.34 ps and 1.90 ps when the NH3-H2SO4 was the catalyst.At the same time,the conversion between the NH3-H2SO4 complex and NH4+/HSO4-ion pair was observed.The CI-NEB mothed indicates that the addition-reaction catalyzed by NH3-H2SO4 is the nearly barrierless reaction(?0.53 kcal·mol-1).In addition,the addition-reaction assisted by NH3-H2SO4 at the air-water interface was simulated.Similarly,the addition-and elimination-reactions were observed.The important finding is that the reaction mechanism different from the gas-phase reaction was discovered.The HOCF2O-ion,an intermediate of the hydrolytic reaction of CF2O,was first discovered and the NH4+/Fand H3O+/HOCF2O-ion were observed in the simulation.This indicates that in the actual atmospheric environment,there are many ways and more complex mechanisms for the catalytic hydrolysis of CF2O molecules at the gas-liquid interface,and these reactions tend to occur in the form of ionic reactions.This is of reference significance for the future study of hydrolytic reaction at the gas-liquid interface in the atmospheric environment.