Electron Momentum Spectroscopy Of Outer Valence Orbitals Of Aldehyde Molecules

The structure and dynamics of atoms and molecules are the most basic problems in atomic and molecular physics.Electron momentum spectroscopy(EMS)is a unique technique for investigating the electronic structure of atoms and molecules,which can directly obtain the binding energy spectrum and the electron momentum profiles for individual orbitals.Since the invention of electron momentum spectroscopy technique,many atomic and molecular systems have been studied.In addition to obtain the momentum distributions for individual orbitals of atoms and molecules,the influence of various physical effects on the electronic structures,such as distorted wave effect,electron correlation effect,molecular vibrational effect have also been explored.Formaldehyde and acetaldehyde were the first identified organic molecules in interstellar space.The search for prebiotic molecules beyond solar system is one of the most exciting topics for astrochemistry since their presence would suggest possible existence of extraterrestrial life.The prebiotic molecules can be synthesized from simple precursors by electron interaction.Therefore,low and intermediate energy electron collision studies on interstellar molecules are of great importance.However,the investigation on electron collision with acetaldehyde and formaldehyde molecules is scarce.In this dissertation,the electronic structure of formaldehyde and acetaldehyde have been studied by a high-sensitivity electron momentum spectrometer.On the one hand,we explained the deviation between the theory and experiment observed for the formaldehyde 2b2 orbital with a theoretical calculation considering vibrational effects.On the other hand,we extend EMS study to valence orbitals of acetaldehyde.The binding energy spectrum and electron momentum profiles for the complete valence orbitals of acetaldehyde have been obtained for the first time.In first chapter,we briefly introduces the basic principles and research progresses of electron momentum spectroscopy.The main content and chapter arrangement of this dissertation are also summarized.In second chapter,the electron momentum spectrometer and experimental methods are introduced.The theoretical framework of electron momentum spectroscopy and some related theoretical methods for electronic structure calculation are also presented.Chapter 3 presents the EMS experiment results of acetaldehyde.The binding energy spectrum and electron momentum profiles for valence orbitals of acetaldehyde are obtained for the first time,and the theoretical momentum profiles with equilibrium geometry and considering vibrational effects are also calculated.Through comparison,it is found that electron correlation effect and molecular vibrational effect have obvious influence on the electron momentum distributions of the valence orbitals of acetaldehyde.The contributions of CH bend vibrational mode v14,CH3 d-stretch vibrational mode v11,CH3 d-deform vibrational mode v5 and CH stretch vibrational mode v4 to the distribution of orbital electron momentum have been analyzed.In addition,the energies and pole strengths for the ionization states of the inner valence orbitals and their satellites of acetaldehyde were also obtained,which were consistent with the SAC-CI general R calculation for the acetaldehyde molecule.Chapter 4 introduces the electron momentum spectroscopy study of formaldehyde.The binding energy spectrum and electron momentum profiles for valence orbitals of formaldehyde are obtained and the theoretical momentum profiles with equilibrium geometry and considering vibrational effects are also calculated.By comparing the experimental measurements with various theoretical calculation results,it is found that the CH2 a-stretch vibrational motion has a significant impact on the electron momentum distribution of the formaldehyde 2b2 orbital,and the long standing controversy between the theory and the experiment has been resolved.In addition,the energies and pole strengths for the ionization states of the inner valence orbitals and their satellites were also obtained,which are consistent with the SAC-CI general R calculation.The last part is the summary of the dissertation and the prospects for future work.