Study On Multiphoton Ionization Via Mass Spectra Of Triethylamine

The laser mass spectrometry is an analytical method of using the laser as an ionizationsource that the material is firstly ionized and then product of the ionization is separated by massto charge ratio, and finally the ion mass peak intensity was measured. It has been40years sincethat people make such method to study organic substances. The method was used not only inorganic chemistry but also in the field of pharmacology, biochemistry, toxicology, foodchemistry, forensic science, petroleum chemistry, geochemistry, environmental pollution, etc..Due to the characteristics of high sensitivity detection, rapid, high-throughput analysis andspecific structural information, the mass spectrometry plays a unique and important role in manyof the current analysis methods. Multiphoton ionization of atoms or molecules absorb one ormore photons, excited to an intermediate quantum state and then further to absorb one or morephotons than the ionization potential and ionization. The process of multi-photon ionization iseasily completed in the strong laser fields, the ionization can be divided into: theresonance-enhanced multiphoton ionization and non-resonance-enhanced multiphoton ionization.Among them, the resonance-enhanced multiphoton ionization of organic matters has prominentposition in exploring and researching high-excited state spectra and photo-ionization dissociationdynamics. Based on triethylamine’s importance in the amines, industry and medicine, the use oflaser mass spectrometry to study its multi-photon ionization dissociation has important referencevalue and practical significance. In this paper, on the basis of previous research, using266nmNd: YAG laser as a light source to study on multiphoton ionization mass spectrometry oftriethylamine molecular, a wealth of triethylamine fragment ion signal was obtained and finallythe experimental results were analyzed thoroughly.This article is divided into four chapters. The first chapter outlines the definition andapplication of laser mass spectrometry, the classification and characteristics of multi-photonionization, the development and characteristics of Nd: YAG laser. The second chapter is theexperimental apparatus and experimental methods. In the chapter, time of flight massspectrometer used in the experiment, the signal detection and data acquisition and processingsystem, the laser system and experimental procedures and methods are described in detail. Thethird chapter is the experimental results and data analysis part. In the first section, firtly, studyingon resonance enhanced two-photon ionization and dissociation principle of triethylaminemolecule, obtains time of flight mass spectrum of the triethylamine molecule. Parent ion andfragment ion reach as much as29kinds. Dissociation principle and the main dissociation channelwas obtained. The dissociation of the triethylamine molecule is the ladder fragmentation patternof the parent ion, belong to class A dissociation mechanism, that is the parent ion loses methyl to get86~+,86~+losesCH2to get72~+,72~+losesCH2to get58~+,58~+losesCH4andthe ethylene molecule to obtain44~+and30~+. Secondly, studying on the index of the lightintensity, find that fragment ions was obtained when one or two photon was absorbed. Finally,the experimental results were verified using the Gaussian software. The experimentalconclusions match with theoretical calculations. In the second section, we find that, by analysis,all of ion peaks of the mass spectrum of triethylamine become strong gradually to maxmum atthe beginning and then weak little by little when the laser beam relative to the delay of the pulsevalve is changed within a certain range and become strong when carrier pressure is increasing.Moreover, making a detailed analysis of the possible causes of the mass peak drift time, findsthat mass spectrometry peak drift may be efforted by the double impact of the grid adsorptionand the instant effect when the ion pass through the grid. Finally, we study the the properties ofthe supersonic molecular beam of triethylamine in the mass spectrometer: the intensity of thesupersonic molecular beam of reaching the ionization center began to fall sharply and tended tolevel off in the end when the distance x between the pulse valve and the skimmer was increasedand was hardly effected when we changed the laser delay time to the pulse valve in the certainrange. The reason is deduced to be the variation of the molecular number density n andtemperature T when the distance x was changed. The numerical simulation of the variation of theintensity of the supersonic molecular beam with x and T also supports the deduction, and isconsistent with the experimental results. The main conclusions and methods of using laser massspectrometry to study triethylamine molecules are summarized in the forth chapter.