| Gas-phase radicals can react rapidly with various gaseous molecules, which play a vital role in catalyzing reactions in atmospheric, combustion and interstellar chemis-try. In this thesis, a combination of flow reactor, flash laser photolysis and synchrotron radiation (SR) photoionization mass spectrometer (PIMS), serves as a universal, mul-tiplexed, selective and sensitive method, ideal for the chemical kinetics study. The synchrotron radiation photoionization mass spectrometer with the advantage of high brightness, high resolution and widely tunability, can detect the intermediates and products in the reaction, sort different structural isomers, and measure the reaction rate coefficients, the ionization energy, the bond energy and et al. Theoretical calcula-tions can predict the geometrical structures and single point energies of the intermedi-ates and products, and can construct potential energy surface for the free radical reac-tion, giving evidences for further study on the reactions mechanisms and atmospheric influences. In the first chapters of the thesis, the flow tube-flash laser photolysis-SR-PIMS apparatus, that shows to be a universal, multiplexed, selective and sensitive method for free radical kinetics, is stalled on the basis of the equipment and technique involved in the Atomic and Molecular Physics Endstation, where the preparatory re-sults are also given. The Cl radical reactions with1-butene and isobutene are studied by utilized the apparatus, which gives out the reaction products and ionization ener-gies. The potential energy surfaces of possible addition and abstraction channels are constructed by theoretical calculations, which exhibit the major addition of Cl to butenes. In chapter five, ground state cyano radical with1,3-butadiene is studied by theoretical calculations, with the construction of potential energy surface and the es-tablishment of favorable channels. In chapter six and seven, the precursor C2Cl2O2and C2Cl4are studied by SR-PIMS. The possible dissociation pathways are discussed under the combination of experimental ionization energy, appearance energies of fragment ions and theoretical calculation. In addition, the experimental results show the cis-conformation parent ion C2Cl2O2+is due to conformational conversion from gauche-conformation parent ion after ionization and the multi-body ion-pair dissocia-tion channels for negative ion Cl are discussed with the help of thermochemistry data.Chapter one, introduction to kinetics of gas-phase radical reactions using pho- toionization mass spectrometry with synchrotron source. Gas-phase radicals can react rapidly with various gaseous molecules, which play a vital role in catalyzing reactions in atmospheric, combustion and interstellar chemistry. A range of experimental tech-niques such as fluorescence and absorption spectrum have been employed to study the reaction processes of gas-phase radicals and acquired some important results. Despite of the sufficient sensibility in the measurement of transient species, most of these techniques are limited to small radicals or molecules, inaccessible to bigger radicals or multiplexed detection. Lately, a combination of flow reactor, flash laser photolysis and synchrotron radiation (SR) photoionization mass spectrometer, serves as a uni-versal, multiplexed, selective and sensitive method, ideal for the chemical kinetics study. Pulsed photolysis laser is used to initiate radical reaction, SR vacuum ultravio-let (VUV) light source ionizes the molecules emerging from the side pinpole and mass spectrometer detects multiple species in the reactions (especially many-atom species). A plenty of original works such as CN, OH and alkylperoxy radical reactions study have been obtained using double-focusing mass spectrometer or time-of-flight mass spectrometer and identified to be potential application in atmospheric chemistry, combustion, interstellar chemistry.Chapter two, introduction to the equipment and technique involved in the Atomic and Molecular Physics Endstation, National Synchrotron Radiation Laboratory, Hefei, China. First, the introduction to the following apparatuses is given, such as the undu-lator providing the tunable vacuum ultraviolet in the main energy range of7.0-22eV, the optic mirrors and performance in the beam line and the rare gas filter. Next, the introduction to the supersonic expansion equipment, aerosol time-of-flight mass spec-trometer and other apparatuses is involved in this section. The theoretical theory and methods are briefly introduced in the last part.Chapter three, introduction to the installation and elementary research of multi-plexed, time-resolved and energy-resolved SR-PIMS. The radical-molecule chemical reactions in a side-sampled flow tubular reactor are initiated by a pulsed photolysis laser and then the gas mixture is sampled via a pinpole and photoionized by continu-ously resonance RF powered Krypton line source or tunable synchrotron radiation VUV photons. The constant flux ions are extracted by a pulsed field at the entrance and detected by the subsequent time-of-flight mass spectrometer. A simple arrange-ment of external trigger laser, pulsed generators and multiscaler enables simultaneous observation of the concentrations of multiple transient or stable species on a millisec- ond time scale. Different structural isomers can be distinguished on basis of the pho-toionization efficiency curves, strengthening the generalization on the reaction mech-anisms. The three-dimensional data structure (intensity as a function of molecular mass, reaction time and photoionization energy) provides multiple images of the chemical reactions under study.Chapter four, introduction to study on the reactions Cl radical with1-butene and isobutene by flow tube-flash laser photolysis-SR-PIMS technique. The mass spec-tra show the existence of addition channels after laser photolysis and the ionization energies for the addition products C4H7Cl are determined to be respective9.58±0.10and9.56±0.10eV. The addition channels proceed via the addition of chlorine to the unsaturated bond of the butenes, leading to the formation of chlorobutyl radicals. The observed addition products have been established mainly via the secondary reactions of chlorine with the forming chlorobutyl radicals.Chapter five, introduction to theoretical study on ground state cyano radical with1,3-butadiene. Theoretical calculations predict the complex isomers C5H6N from CN collision with1,3-butadiene, isomerization processes and product formation of C5H6N, and the favorable channels in the reaction.Chapter six, introduction to study of precursor C2Cl2O2by SR-PIMS. The possi-ble dissociation pathways are discussed under the combination of experimental ioni-zation energy of C2CI2O2, appearance energies of fragment ions and theoretical CBS-QB3and W1u methods. In addition, three conformers of C2Cl2O2+ion, namely trans-, gauche-and cis-conformer are investigated by using CBS-QB3and Wlu methods, which suggest the existence of the cis-conformation parent ion CaCl2O2is consistent with the second onset at11.6eV in the experimental PIE curve and the as-sociated calculations. The dominant fragment ion CC1O+is mainly originated from direct cleavage of the elongated C-C bond in the trans-conformer parent ion after ionization.Chapter seven, introduction to study of precursor C2Cl4. The ionization energy of C2Cl4, appearance energies of fragment ions and preferred dissociation pathways near the threshold energies are studied by experimental and theoretical methods, with the assignment of spectral vibration progression v2in the photoionization curve of the parent cation. The negative ion Cl" from ion-pair dissociation channel are observed and discussed to be related to the multi-body ion-pair dissociation with the help of thermochemistry data. |
PDF Full Text Request