| As a large number of organic compounds,nitrogen-containing aromatic compounds are widely used in dyes,pesticides,pharmaceutical intermediates,and bioengineering.In the process of photoionization,CH2NH elimination is generated mainly by McLafferty rearrangement,that is,during the cleavage of the ?C-?C bond,the y-H atom migration occurs through the six-membered ring transition state.Using the advantages of continuously adjustable light energy in synchrotron radiation and soft ionization,the photoionization efficiency spectrum(PIE)is obtained by scanning the photon energy to obtain the ionization energy(IE)of the molecule and the appearance potential(AE)of ionized fragments,which contributes to better understand the photoionization and photodissociation mechanisms of these molecules.In this dissertation,tryptamine,phenethylamine,imidazole,and indole molecules were selected as the research system.Synchrotron radiation vacuum ultraviolet photoionization mass spectrometry(SVUV-PIMS)experiments were combined with quantum chemistry calculations to study the photodissociation mechanism of nitrogen-containing aromatic compounds..The mass spectrum of each molecule was obtained by mass spectrometry to obtain the mass number of the photoionized product,and then analyzed the molecular formula of these fragments.The photon energy was scanned to obtain the PIE of the molecular matrix and the fragments,determining the ionization energy of the molecule and the potential of the fragment.The IE values of the molecular matrix were also obtained by quantum chemistry calculation.The possible dissociation paths of ionized ions were further calculated,possible dissociation fragments and their AE values were obtained,and the experimental results were compared to verify the rationality of the calculation.Based on theoretical calculations,the photodissociation mechanism of these molecules was explored.The first chapter introduces the nitrogen-containing aromatic compounds and the two mechanisms involved in this dissertation.Firstly,the classification of nitrogen-containing aromatic compounds and its application in various aspects are introduced.Secondly,the development of McLafferty rearrangement mechanism and the application and rearrangement effects of this rearrangement mechanism on carbonyl compounds are introduced.Furthermore,the roaming mechanism and its application in pyrolysis and photolysis of small molecules such as formaldehyde and acetaldehyde are introduced.The second chapter introduces the experimental and theoretical calculation methods required in this paper.Firstly,the synchrotron radiation experimental device and laser desorption technology are introduced.Secondly,the theoretical calculation methods used in the dissertation are introduced,including the combined high-precision energy calculation method G3B3 and the LC-BLYP density functional theory method used in the scan-bond dissociation process.In the third chapter,the photoionization and photodissociation of tryptamine molecules were studied using the above experimental and calculation methods.The tryptamine molecules were detected by laser desorption/vacuum ultraviolet photoionization mass spectrometry(LD/SVUV-PIMS)technique to study the photoionization process of tryptamines in the gas phase.The ionization energy of the parent ion and appearence ennergy of fragmentation ions were obtained.Using G3B3 method to calculate those energy.Comparing the experimental values,the AE value of the tryptamine CH2NH elimination fragment(m/z=131)obtained based on the traditional McLafferty rearrangement mechanism was 9.36 eV,which was significantly higher than the experimental value of 8.22 eV.Considering the roaming mechanism of the photolysis process of small molecules such as formaldehyde,the effect of roaming was added to the McLafferty rearrangement reaction of the tryptamine photodissociation process,that is,during the CH2NH2 group in the cleavage process of the C-C bond,the H atom was directly transferred to the aromatic ring by the roaming reaction and then dissociated to give a m/z=131 fragment.The calculated ionization energy was 8.33 eV,which was very close to the experimental value.It shows that the McLafferty rearrangement mechanism modified by the roaming effect is more reasonable.The LC-BLYP/6-311G(d,p)was further used to calculate the C-C bond cleavage process of the tryptamine molecule,and the rationality of the presence of the roaming reaction in the McLafferty rearrangement was proved.In Chapter 4,the photoionization and photodissociation of phenethylamine were studied.The photodissociation of phenylethylamine positive ions was studied using SVUV-PIMS combined with laser desorption.The IE and fragment AE values of phenethylamine were obtained by scanning the photon energy.The IE value of phenylethylamine and the photodissociation reaction path were calculated by G3B3 method,and the reaction pathways of different fragments were obtained.Consistent with the tryptamine molecule,the AE with m/z=121 was closer to the experimental value after considering the roaming effect.In Chapter 5,the photoionization/photodissociation process of imidazole and indole was studied using infrared laser desorption combined with SVUV-PIMS technology.The photoionization spectra of imidazole(C3H4N2)under different photon energy were measured.C2H3N+(m/z 41)fragment ion was obtained at low ionization energy and N2H4+(m/z 32),N2H3+(m/z 31)and CH3+(m/z 18)fragment ions were obtained at higher ionization energy.By scanning the PIE curve of the C3H4N2-ion,the measured ionization energy of the imidazole was 8.70 eV.The photoionization mass spectrum and photoionization efficiency spectrum of indole(C8H7N)were measured under different photon energy.The IE values of the parent CsNH7+(m/z 117)and the AE values of fragment ions such as C7H6+(m/z 90)were obtained,and possible photodissociation paths were estimated based on the dissociation law.Experimental data was provided for the photoionization and photodissociation of imidazole and indole. |
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