Study On The Reaction Mechanism Of C₃O₂ With Interstellar And Atmospheric Free Radicals

C₃O₂ is one of the important carbon sources in the atmosphere and plays an important role in interstellar,atmospheric and experimental synthesis.The ability of C₃O₂ to interact with some small molecular systems affects the rate of formation and elimination of these molecules in interstellar and atmospheric environments.According To Statistics,free radicals account for more than 20%of the total interstellar molecules.Therefore,free radicals play an important role non only in the abudances of interstellar chemistry and atmospheric chemistry,but in the reactions involved in interstellar and atmospheric chemistry.However,there are few studies on the reaction mechanism of C₃O₂ with free radicals.More importantly,the mechanism and processes of how free radicals attack and affect the existence life of C₃O₂ have not been reported in detail.One obvious reason is that C₃O₂ is highly susceptible to polymerization,which makes it difficult to study its reactions with other molecules（let alone more reactive radicals）experimentally.In this paper,we use the B3LYP method in the density functional to obtain the geometric structure and vibration frequency of each intermediate,transition state,reactants and products of a series of free radicals reacting with C₃O_2,and use the high-level combination algorithm CBS-QB3 method to obtain the detailed energy information.The attack site and reaction path of C₃O₂ with a series of free radicals（σ-type andπ-type）were described from the microscopic point of view.At the same time,the correlation between the rate-determining step obtained by the reaction of C₃O₂ with free radicals and the dimerization energy and electron affinity potential of free radicals was analyzed in detail.Results are as follows:（1）In most cases,the rate-determining step of the reaction between C₃O₂ and free radicals is the process of free radical attacking the central carbon of C₃O₂.（2）Relationship between the rate-determining energy for the reaction of C₃O₂ withπ-type radicals（C-attack）and the dimerization energy of these radicals（C-attack）is 0.9833.The rate-determining energy of the reaction between C₃O₂ and the free radical with N/O as the attacking atom also has a good correlation with the dimerization energy of the free radical,which are 0.8058 and 0.9723,respectively.（3）Relationship between the rate-determining energy for the reaction of C₃O₂ with hydroxides of these radicals of C-Si,N-P and O-S atoms and the electron affinity of these radicals is 0.8098.The correction between rate-controlled energy barriers for the reaction of C-attrack radicals which F,Cl,Br are as the attacking ligands with C₃O₂ and the electron affinity of these radicals were 0.9505,0.9860 and0.9949 respectively.For the same halogen,the electron affinity value increases with the increase of the number of halogens,and the corresponding rate-control energy barrier decreases gradually.（4）The correlation of kinetic energy barrier of the central C addition reaction of C₃O₂ with free radicals and the kinetic energy barrier of the outer C addition reaction of C₃O₂ with free radicals is 0.8618.（5）The free radicals in the interstellar and atmosphere are easy to react with C₃O₂ and promote the decomposition of C₃O₂.In this paper,the discussion of correlation is helpful for us to quickly judge the degree of difficulty or ease of reaction between free radical and C₃O₂.Through the detailed study on the reaction mechanism of C₃O₂ and a series of free radicals,it provides theoretical data for the existence and disappearance of C₃O₂and the traceback of interstellar or atmospheric carbon sources.