Certain Molecular Configuration Like The Relative Stability Of The Isomers Of Electron Momentum Spectroscopy Study

In this thesis,the electron momentum distributions for the complete valence molecular orbitals of ethanol,ethylamine and 1-butene are investigated.Two relative stable conformes coexist in thermal equilibrium at the room temperature for all of these three molecules.On the one hand,the electron momentum distributions of the ethanol,ethylamine and 1-butene and the difference in electron structures between their conformers due to the internal rotation are carried out in the present work.On the other hand,the relative abundances and Gibbs free energy difference of the conformers are obtained by comparing the experimental and mixed theoretical electron momentum profiles.The charge transfer accompanied with the hyperconjungation effect is observed in the highest occupied molecular orbitals (HOMO)of ethanol and explained by means of natural bond oribtal(NBO)theory. For further investigation,the binding energy spectra for outer-valence orbitals are obtained with the high-energy-resolution energy-momentum-dispersive multichannel spectrometer.This thesis includes five chapters as follow:The first chapter includes the basic principle and applications of the electron momentum spectroscopy as well as the introduction of the second generation and the third generation of the electron momentum spectrometer.The second chapter introduces the category of the isomers and the various experimental methods applied to study the phenomena of isomers.In the third chapter,the electron momentum distributions for the complete valence orbitals of ethanol have been investigated by the noncoplar symmetry electron momentum spectrometer.The experimental momentum profiles(XMPs)are compared with the theoretical momentum profiles(TMPs)calculated with DFT-B3LYP and DFT-G96LYP methods combining 6-311++G^**,aug-cc-pVDZ basis sets.We found that the TMPs are all in good agreement with the experimetal data.As for HOMO,TMPs calculated with methods using the basis sets without diffuse functions underestimate the experimental data in the region of p＜0.8 a.u..On the other hand,the relative abundances of the two conformers of ethanol has been determined by comparing the XMPs with the Boltzmann-weighted TMPs of the 7a'/7a orbitals.The relative abundances are 81±3%,19±3%,for the gauche-ethanol and trans-ethanol respectively and the relatvie Gibbs free energy difference△G_g-t= -0.40±0.10 kcal/mol.Our conclusion is that the gauche-ethanol is more stable than the trans-ethanol at the room temperature.Furthermore,the charge transfer accompanied with the hyperconjuncation effect of the ethanol has been observed and explained with the NBO theory.Finally,the binding energy spectra for the outer valence orbitals and electron momentum distribution for the HOMO of the ethanol have been obtained by the electron momentum spectrometer with high-energy resolution.The ionization peak of the 9a orbital of gauche-ethanol is observed.The assignment of the orbitals is carried out and the ionization energy is 15.35 eV(9a),which is consistent with the results of OVGF calculation(15.50 eV(9a)).In the fourth chapter,the electron structures of the complete valence orbitals of ethylamine have been investigated by the noncoplar symmetry electron momentum spectrometer.The XMPs of the valence orbitals for ethylamine have been obtained for the first time.The XMPs are compared with the TMPs which calculated by DFT-B3LYP and DFT-G96LYP methods with 6-311++G^**,aug-cc-pVDZ basis sets. In general,the theoretical results are in better agreement with the experimental data. On the one hand,by comparing the XMPs with the Boltzmann-weighted TMPs of 1a"/7a orbitals,the relative abundances of two conformers of ethylamine are 59±4% (gauche-ethylamine) 41+4%(trans-ethylamine).The relative Gibbs free energy difference△G_g-t=0.19±0.10 kcal/mol.On the other hand,The ordering of the orbitals: 9a,8a(gauche-ethylamine);7a',2a"(trans-ethylamine)are determined by comparing the XMPs with theoretical ones for the different sets of assignments.The conclusion in the order of increasing ionization energy is 9a＜8a(gauche-ethylamine);7a'＜2a"(trans-ethylamine) Finally,the ionization energies and electron momentum profiles of ethanol and ethylamine are compared.The HOMO characters of the two molecules have been investigated.The difference between the ionization energies of HOMO for ethanol and ethylamine are well explained by NBO theory.The fifth chapter introduces the electron momentum distributions of the complete valence orbitals for 1-butene.The TMPs is calculated by DFT-B3LYP and DFT-G96LYP methods with 6-311++G^**and aug-cc-pVDZ basis sets.All of the TMPs show no difference and are in good agreement with the XMPs.the relative abundances and the relative Gibbs free energies of the conformers for 1-butene have been determined by electron momentum spectroscopy.The relative abundances are 65±3%,35±3%,for the skew-1-butene and syn-1-butene respectively.The relative Gibbs free energy difference△G_skew-syn=-0.37±0.10 kcal/mol.