Synchrotron Photoelectron-Photoion Coincidence Spectroscopy Of Molecules And Radicals

Free radicals are important intermediates and play essential roles in atmospheric reactions.Due to their very low concentrations it is challengent to investigate radicals in experiments.Fundamental data of spectroscopy and structure of radicals are still very limited.Taking advantages of vacuum ultraviolet synchrotron radiation,coincidence mass spectrometry and threshold photoelectron spectroscopy,Synchrotron threshold photoelectron photoion coincidence time-of-flight mass spectrometry?synchrotron TPEPICO TOF-MS?analyzes threshold photoelectrons and their corresponding photoions in coincidences,which is effective to investigate photoionization of organic molecules and their related radicals.In this dissertation,photoionization and dissociative photoionization of molecules and radicals were investigated to acquire precisely their corresponding thermodynamic parameters such as the ionization energies of molecules and radicals and the appearance energies of fragmental ions via synchrotron TPEPICO TOF MS.The dissertation mainly includes the following parts:1.Threshold photoelectron spectroscopy?TPES?of CH₃ radical.A flash pyrolysis micro-reactor,based on the supersonic molecular jet cooling technology,was constructed to produce free radicals with high yield.The CH₃ radical,as a demonstration research system,was produced from the pyrolysis of CH₃NO2 molecule.And the adiabatic ionization energy of CH₃ radical was measured precisely to be 9.84 + 0.01 eV via the TPES.Meanwhile,vibrational excitations belonging to the umbrella mode with hot bands was identified in the TPES of CH₃ radical.2.Investigation of the pyrolysis of n-C₄H₁₀ molecule.Products from the pyrolysis of n-C₄H₁₀ molecule were detected through TPEPICO TOF-MS,including CH₃,C₂H₅,C3H7,C2H4 and C₃H₆.Here,C3H7 radical produced from the pyrolysis of n-C₄H₁₀ molecule was directly and successfully identified in the experiments for the first time.Adiabatic ionization energy and vertical ionization energy of C₂H₅ were measured accurately to be 8.20±0.01 eV and 8.70 ±0.01 eV,respectively.And the vibrational excitations belonging to the pyramid mode were also identified in the TPES of C₂H₅ radical.Meanwhile,adiabatic ionization energy of C₃H₆ molecule was precisely measured to be 9.75 ±0.01 eV and the vibrational excitations belonging to the stretch mode were identified in the TPES of C₃H₆ molecule.In addition,quantum chemical calculations were carried out to form the potential energy surface related to the thermal decomposition of n-butane and several transition states of n-C₄H₁₀ molecule were found through the intrinsic reaction coordinate calculations.With the results of experiments and theoretical calculations,a clear picture of the dissociation mechanism has been revealed.3.Investigation of the dissociative photoionization of n-C₄H₁₀ molecule.The n-C₄H₁₀+?parent ion and some fragement ions such as C2H4+ and C₃H₇⁺ were identified via TPEPICO TOF-MS.Adiabatic ionization energy of n-C₄H₁₀ molecule was precisely measured to be 10.51 ±0.01 eV via the TPES.Besides,adiabatic appearance energy of the C₃H₇⁺ ion was identified to be 11.31 ±0.01 eV with experimental measurement and satisfied simulation.And theoretical calculations were also carried out to verify the experimental results.4.Investigation of the dissociative photoionization of p-,m-,o-C₇H₇Br molecule.The p-,m-,o-C₇H₇Br+ parent ions and corresponding fragment C₇H₇+ ions were detected via TPEPICO Time of flight mass spectra,respectively.According the TPES measurement,adiabatic ionization energy of the p-,m-,o-C₇H₇Br molecule were precisely measured to be 8.68 ±0.01 eV,8.82 ±0.01 eV and 8.78 ±0.01 eV,respectively.Besides,appearance energies of the fragment C₇H₇+ ions from the dissociative photoionization of the p-,m-,o-C₇H₇Br molecule were also accurately identified to be 11.46±0.01 eV,11.55±0.01 eV and 11.40±0.01 eV,respectively.According to the theoretical calculations and comparisons between experimental results and previous work,it was concluded that p-,m-,o-tolyl ions could be the exclusive configuration type of the fragment C₇H₇+ ions produced from the dissociative photoionization of p-,m-,o-C₇H₇Br molecule,respectively,which was different from the dissociation of p-,m-,o-C₇H₇Br+ ions.