Development Of Liquid Microjet Photoelectron Imaging Equipment And Ultrafast Relaxation Dynamics Of Difluoroaniline

Water is the basis of all life,and almost all physiological and chemical reactions occur in an aqueous environment.So the study of aqueous solutions helps us understand the physical and chemical processes that occur in life.The direct measurement of correlated electrons in aqueous solutions is key to understanding these processes,since electrons carry the characteristic information of molecular structure,energy and orbital coupling before and after reaction.At present,the photoelectron spectroscopy method based on liquid microjet at home and abroad can only measure the kinetic energy of photoelectrons,but cannot measure its angular distribution,which contains important information such as molecular orbital symmetry,orbital characteristics,and molecular orientation.Compared with the mature gas phase photoelectron spectroscopy and imaging,the imaging method for measuring photoelectron angle distribution in solution has always been technically difficult.Based on this,we build a liquid microjet photoelectron imaging equipment that can measure the electron kinetic energy and angular distribution in liquid environment,and realized the measurement of the photoelectron image of furfural aqueous solution.The main research work of this thesis is as follows:(1)A liquid microjet time-of-flight mass spectrometer has been built to measure the mass spectrum of sample molecules in aqueous solutions.The mass spectra of acetone,aniline and cytidine in gas phase and aqueous solution are studied at 800 nm and 266.7 nm,respectively.The results show that the parent molecules in the solution are easy to be broken,and show the characteristics of binding with water molecules,which clarifies the mechanism of molecular fragmentation from dissociative ionization.(2)The liquid microjet sampling technology is developed and combined with the velocity map imaging technology to build a liquid microjet photoelectron imaging equipment.The photoelectron kinetic energy and angular distribution of furfural in liquid environment are measured,and the adiabatic ionization energy of furfural in aqueous solution is 8.46 eV.(3)A 160 nm femtosecond vacuum ultraviolet laser pulse is generated by four-wave mixing technology,with output of single pulse energy of 69 nJ/pulse.The time-of-flight mass spectra of CH3I ionized by 160 nm femtosecond vacuum ultraviolet laser are measured.(4)Ultrafast dynamics of 2,5-difluoroaniline and 3,4-difluoroaniline.The vibrational coherence between the S1 band origin and the X10 mode at 289.8 nm excitation of 2,5-difluoroaniline is observed by time-resolved photoelectron imaging.Combined with theoretical calculations,the excitation state relaxation dynamics involved and the accompanying periodic real-time evolution of molecular structure are tracked,and the phase inversion of different photoelectron spectrum components is explained.However,no vibrational coherence was observed in 3,4-difluoroaniline.When the molecule is excited near the S1 band origin,it will first move away from the Franck-Condon region,and when the molecule is in the S1 high vibration level,the intramolecular vibration energy redistribution process will occur.In addition,the intersystem crossing from S1 state to triplet state and the continuous evolution in triplet state will occur at both excitation wavelengths.The obvious difference in dynamics between the two molecules may be caused by the different positions of fluorine atoms on the benzene ring.