Mass-selective Negative Ion Beam-Time-of-flight Mass Spectrometry System

Negative ions are widely present in interstellar,atmospheric,plasma and other environments.Since negative ions are generally affected by the short-range Coulomb potential and the electron affinity is low,negative ions exhibit many different properties from neutral and positive ions.The research on the structure of negative ions,electronic states and dynamic processes is helpful to understand the physical processes such as low-energy electron-molecule collisions and dissociative attachment.It has become a very important research direction in the field of atomic and molecular physics.In this thesis,we have self-designed and established a negative ion beam-Time-of-flight mass spectrometry,and carried out some preliminary research using the system.The main content and results of the thesis are as follows:We have self-designed and established a negative ion beam-Time-of-flight mass spectrometry system.We have described in detail each component of the system,including vacuum system,negative ion beam source,negative ion extraction system,laser-negative ion interaction zone and detection system.Using the SIMION program,we have simulated the performance of the system,including electron beam focusing,negative ion number density estimation,electrostatic lens focusing,ion flight time,and mass resolution.The effect of different parameters on the system performance was investigated which would provide valuable information for further experimental studies.On the established experimental device,a preliminary study of electron-SF₆molecular collision was carried out.The yields of positive ions and neutral excited states produced by SF₆ molecules colliding with electrons were measured with electron energy up to 400 eV.The dependence of positive ion signal on the electron energy is consistent with the total ionization cross sections reported in the literature.In the future,based on this device,in-depth research will be conducted on the interaction between negative ions and ultrafast laser fields.