Time-delayed Time-of-flight Mass Spectrometry For The Low-Energy Electron Impacts With Liquid Surface

Recently,electron-induced or-driven chemical reactions receive much attention.Liquid and its surface are the other essential venues of chemical reactions.Unfortunately,little is known about the electron-induced reactions in the liquid and on the liquid surface.We set up a time-delayed time-of-flight mass spectrometer to investigate the tow-energy electron impacts with liquid surface.The apparatus consists of a pulsed lbw-energy electron gun,a cylindrical liquid beam emits as the laminar flow from a microjet,a linear time-of-flight mass spectrometer,and the detector.By using the present apparatus,we can investigate the electron-impact ionization dissociation and electron-induced reactions on the liquid surface.Here we describe a time-delayed mass spectrometry.Usually a negative pulse is added on the skimmer,which is used as the ion extractor as well as the vacuum baffle,to collect the positively charged products.A pulse voltage on the ion extractor is delayed with different intervals with respect to the incident electron beam pulse.We can identify the cationic fragments produced on the liquid surface by delaying the ion extractor pulse.This method's sensitivity are proved in the experiments of the gas-phase.In comparison with the gas-phase experiments,the ion peaks become much broader in the mass spectra of the ethanol liquid beam,primarily due to the molecular evaporation and diffusion,as well as the ion-molecule reactions.On the basis of the time-delayed mass spectra,we find that the hydrocarbon ions are the predominant products from the liquid surface.These hydrocarbon ions are closety related to the molecular ethanol orientation on the liquid surface,nacety,the CH3-CH2-group of ethanol prefers to be outside the surface.This surface picture of liquid ethanol has been widely accepted on the basis of the sum frequency generation(SFG)experiments and molecular dynamics simulations.