Slow Electron Velocity-map Imaging Study On Photoionization Of Excited State Of M-bromofluorobenzene

In this thesis,we investigate the photoionization of excited state of m-bromofluorobenzene（m-BrFPh）by using one-color resonant two-photon ionization（1C-R2PI）,slow electron velocity-map imaging（SEVI）methods and high-level theoretical calculation.In the SEVI experiment,we introduced a new image processing method,which effectively reduced the ultraviolet electron noise in the process of two-color resonant two-photon ionization（2C-R2PI）.And the signal-to-noise ratio has been improved greatly in the SEVI spectra.Based 1C-R2PI and SEVI techniques,we respectively obtained the（1+1）REMPI spectra in S₁ state and SEVI spectra in D₀ state of m-BrFPh.The first adiabatic electronic excitation energy(36987±4 cm^-1)and adiabatic ionization potential(73903±8 cm^-1)have been acquired.The geometries,frequencies and molecular orbitals of m-BrFPh were analyzed by utilizing quantum chemistry method.In addition,Franck-Condon simulation of REMPI and SEVI spectrum for m-BrFPh were performed.The computed frequencies are in excellent agreement with the experimental observations,which aids us to confidently assign major vibrational modes in S₁ and D₀states.Furthermore,the mixing of vibrational modes in both between S₀&S₁ and S₁&D₀ states was discussed.In the SEVI experiment,photoelectron angular distribution（PADs）of m-BrFPh has been measured in the near-threshold ionization.The anisotropy parameter（β₂）decreases drastically to negative value with the increase of electron kinetic energy.In the near-threshold ionization,it is suggested that the shape resonance exists for the photoionization of m-BrFPh.