The Setup Of Gas Phase Ion Dynamics Expriment

The reactions between ions and molecules play an important role in atmospheric chemistry,interstellar chemistry,combustion reaction and other chemical reactions,and the reactions between ions and molecules are also an important branch of chemical reactions.In the microscopic field of chemical reaction,the cross beam method is a powerful means to study the scattering and collision of reaction in order to obtain the accurate information of reaction kinetics.The cross beam method,combined with high-resolution detector,ion velocity imaging and other experimental techniques,can obtain the velocity distribution and angular distribution of the reaction products.Through the analysis of velocity distribution and angle distribution,we can get the kinetic information of reaction,such as reaction cross section,reaction mechanism,reaction constant and so on.Compared with the neutral cross molecular beam reaction,there are few studies on the cross molecular beam reaction,and there are still many places to study the micro mechanism of this kind of reaction.It is difficult to obtain high-resolution product distribution in ion molecule cross beam reaction due to the difficulty of obtaining ion beam with narrow velocity broadening.In order to prepare the ion beam with cold internal temperature and narrow velocity distribution,it is necessary to guide and screen the ion reactants in the path from the generation of ion beam to the reaction,so as to ensure the intensity and collimation of the ion beam source.Therefore,the author participated in the construction of a set of high-resolution experimental instruments to study the collision scattering experiment of ion molecules,and completed the test and optimization of the whole system.The system adopts a multi-stage differential pumping structure to ensure the vacuum of the scattering region and optimize the signal-to-noise ratio.The ion beam is collimated into quadrupole mass spectrometry by skimmer.Quadrupole mass spectrometry can be used for ion guidance and mass charge ratio screening.Then,under the guidance of the guide lens,the selected ion beam enters the ion trap and is cooled by colliding with the buffer gas under the action of the helium cold head.The temperature of the ion trap can be reduced to close to the temperature of liquid helium.Then,the ions are extracted from the ion trap by the fast response pulse high pressure and enter the reaction chamber to collide with the molecular beam.The reaction products fly to the detector under the action of the special ion lens.The detector with position response and time resolution can image the velocity of product ions and obtain the kinetic information of reaction.This new instrument uses ion trap combined with cold head to trap and cool the ion beam,which has a very good control of the ion beam velocity broadening and velocity.At the same time,it combines the cross beam and velocity imaging method to study the gas phase ion dynamics,which greatly increases the reaction kinetics information we can obtain.