Reaction Kinetics Of Two Small Alkyl Radicals With Oxygen

Atmospheric free radical chemistry is the core of the study on the causes of atmospheric complex pollution.In the process of atmospheric oxidation,hydrogen capture reaction or addition reaction between volatile organic compounds and oxidants such as OH,O3,and the generated free radicals react with O2 to produce peroxy radicals.Under polluted atmospheric conditions such as cities,peroxyl radical RO2 will react with NO,,and its product NO2 will increase the concentration of O3 in the atmosphere under solar photolysis,while the product organic nitrate will make the secondary organic aerosol in the atmosphere.Under clean air conditions such as rural area,peroxy radical RO2 will react mainly with HO2,RO2 itself or other peroxy radicals to produce lower volatile organics like aldehydes,ketones and other substances,thus promoting the formation of secondary organic aerosols in the atmosphere.Atmospheric oxidation determines the formation and removal of the major secondary pollutants in the atmosphere and is primarily determined by the free radical chemistry in the troposphere.The study of atmospheric free radical chemical reactions is of great significance for understanding photochemical smog,fine particle formation and smog exploration.Based on vacuum ultraviolet photoionization time-of-flight mass spectrometry,combined with microwave discharge and a flow tube reactor,the research platform of atmospheric free radical chemical reaction was developed,and the reaction kinetics of several alkane radicals with oxygen were studied.In this thesis,utilizing the vacuum ultraviolet photoionization mass spectrometry atmospheric free radical chemical reaction research platform,where a vacuum ultraviolet discharge lamp was employed as ionization source,the self-reactions of methyl radical(CH3)and ethyl radical(C2H5)in the flow tube were investigated.Their concentrations were quantitatively measured,and then their reaction rate constants with OZ at normal temperature and low pressure were determined.The synchrotron radiation at Hefei was used as the ionization source to detect the reactants and products in the flow tube.The photoionization efficiency spectrum can be used to discriminate the photoionization and photodissociation ionization processes,and distinguish different isomers.Then with the help of theoretical calculations,the detailed reaction mechanism in the flow tube was suggested.The research content of this thesis mainly includes the following parts:1.Development of a research platform for atmospheric free radical chemical reactions by vacuum ultraviolet photoionization mass spectrometry.F atom was produced by microwave discharge device,free radical was prepared in a flow tube reactor,and its chemical reaction was studied.The reactants and products were detected by a home-made vacuum ultraviolet photoionization time-of-flight mass spectrometer.The mass resolution of the spectrometer is determined to be M/?M-2100.The detection of limit of stable species such as benzene series is 0.8 ppb,and the detection of limit of active species is about 1.5 ppb.The experimental results also show that the F atoms reacts with the flow tube itself.In addition to the known product SiF4,a series of fluoro-silicone products such as SixOyFz are found for the first time.2.Quantitative measurement of CH3 and C2H5 radical concentrations by photoionization mass spectrometry.The self-reaction experiments of CH3 and C2H5 radicals were carried out by vacuum ultraviolet photoionization mass spectrometry.Combined with the known self-reaction rate constants in the literatures,the signal intensity of the free radicals in mass spectra was calibrated,and the absolute concentration of free radicals was obtained in real time.In addition,according to the photoionization cross-section values of free radicals and NO gas,the concentration of free radicals was measured in combination with the concentration of known NO gas.The results were consistent with the self-reaction experiments,and the feasibility of measuring the free radical concentration from the self-reaction experiment was verified.3.Reaction kinetics of CH3 with O2.The kinetics of important CH3 and O2 reactions in the atmosphere were studied by vacuum ultraviolet photoionization mass spectrometry atmospheric free radical chemical reaction research platform.The F atoms generated by microwave discharge reacts with methane to generate CH3 radical,and the synchrotron radiation at Hefei is used as the ionization source.The products of CH3 and O2 reaction systems are detected by photoionization mass spectra and photoionization efficiency curves to distinguish isomers.The ionization energy IE(CH3O2)= 10.33 ± 0.05 eV of methyl peroxy radical CH3O2 was accurately measured,which is consistent with previous results.The products of the reaction of CH3 with O2,the self-reaction of CH3 and the self-reaction of CH3O2,and some secondary reactions were obtained in the experiments.The mechanism of free radical chemical reaction in the flow tube was suggested.Combined with the simulation results,the experimental conditions of the CH3 and O2 reaction systems were optimized,and the rate constant of the reaction was obtained.At room temperature 298 K and 2 torr gas pressure in the flow tube,k(CH3+O2)=(3.2 ± 0.2)*10-14 cm3/molecule s.4.Reaction kinetics of C2H5 with O2.The kinetics of the important C2H5 and O2 reactions in the atmosphere were studied by vacuum ultraviolet photoionization mass spectrometry atmospheric free radical chemical reaction research platform.With photoionization mass spectra and photoionization efficiency curves,the products of C2H5 and O2 reaction systems were detected,the isomers were distinguished,and the photoionization and photodissociation ionization processes were distinguished.The appearance energy of C2H5+ fragment ions generated from dissociative photoionization of C2H5O2 was accurately measrured,AE(C2H5+)= 10.05± 0.05 eV.The photoreaction efficiency spectrum is also used to distinguish the primary reaction and the secondary reaction products in the flow tube.The C3H6+and C3H7+ions are all derived from the dissociative photoionization of the secondary reaction product C4H10 and the freedom in the flow tube reactor.The basis reaction mechanism was studied.Combined with the simulation results,the experimental conditions of the C2H5 and O2 reaction system were optimized,and the rate constant of the reaction was obtained.At room temperature 298 K and 2 torr gas pressure in the flow tube,k(C2H5+O2)=(2.1±0.2)*10-12 cm3/molecule s.