Building Of High-resolution Time-of-flight Mass Spectrometer With Photoelectron Velocity-map Imaging Apparatus And Slow Electron Velocity-map Imaging Study On Photoionization Of Excited State Of Aromatic Molecules

In this thesis,we investigate the photoionization of excited state of aniline,styrene,4-methylstyrene and?-methylstyrene using the resonance-enhanced multiphoton ionization?REMPI?and slow electron velocity-map imaging?SEVI?methods.In order to study the spectroscopy and dynamics of molecules in gas phase,we design a high-resolution time-of-flight mass spectrometer with photoelectron velocity-map imaging apparatus.The energy resolving power has been improved by the electric field compensator in electron optics.The samples of xenon and aniline have been photoionized to test the performance of the apparatus.The results show that the mass resolution of time-of-flight mass spectrometer is above 1300;the energy resolution of the imaging apparatus is 2.19%and the threshold energy resolution of better than 1meV.The S₁ state REMPI spectra and D₀ state SEVI spectra of aniline,styrene,4-methylstyrene and?-methylstyrene have been assigned with the aid of high-level theoretical calculations.The vibrational frequencies,excitation energies of S₁ state and adiabatic ionization energies of D₀ state are precisely measured.For aniline,non-planar geometry of S₁ state is revealed with the experimental and theoretical results.The excitation energy and ionization energy of aniline are determined as 34031±3cm^-1 and 62271±6cm^-1.For styrene,the high-frequency vibronic structures of REMPI and SEVI spectra are assigned for the first time and the frequencies of some controversially vibrational modes are determined.The excitation energy(34759±3cm^-1)and ionization energy(68267±6cm^-1)have been achieved.For 4-methylstyrene,the 5e?1e methyl torsional transition is first observed in REMPI spectrum and it is the first time to report the ionization energy(65872±6cm^-1),frequencies of methyl torsional levels of D₀ state and the assignment of REMPI and SEVI spectra.For?-methylstyrene,six Franck-Condon progressions in the REMPI spectrum have been assigned for the first time and the excitation energy is determined to be 35072±3cm^-1.In SEVI technique,photoelectron angular distribution of aniline,styrene and4-methylstyrene have been measured.The anisostropic parameters are extracted from the photoelectron angular distribution,and further the variation of anisotropy parameters of D₀0⁰state with photoelectron kinetic energy is investigated.The shape resonance in the near-threshold ionization of aniline and 4-methylstyrene has been revealed.