Freon Molecules In High-energy Resolution Electron Momentum Spectroscopy

In this thesis, electron momentum distributions of outer valence orbitals of difluorodichloromethane (CF₂Cl₂) are investigated by using the binary (e,2e) spectrometer, especially the newly developed high-energy-resolution energy-momentum-dispersive multichannel spectrometer. By directly comparing the experimental momentum profiles with the theoretical ones, unambiguous conclusion of orbital ordering of this molecule are drawn. Furthermore, the first electron momentum spectroscopy (EMS) study of CFCl₃ has also been performed using an energy-dispersive multichannel (e, 2e) electron momentum spectrometer. In addition, the electron momentum distributions of the outer valence orbitals of CF₃Cl, CF₂Cl₂ and CFCl₃ are compared, and the orbital characters for these series molecules have been discussed.This thesis includes four chapters as follow:The first chapter introduces the theoretical background, the application of EMS, the energy-dispersive multichannel spectrometer and especially newly developed high-energy-resolution energy-momentum-dispersive multichannel spectrometer.The second chapter introduces the EMS study of the outer valence orbitals of CF₂C₂. We obtained the experimental electron momentum distributions and compared with the theoretical calculations of DFT-B3LYP method using different basis sets to study the effects of the basis sets. In general, 6-311++G basis set give the best description of the experimental results. We also compared the experimental electron momentum distributions with calculations using HF and DFT (with different functionals) methods with 6-311++G basis set to study the influence of different theoretical methods. In general, DFT-SVWN5/6-311++G calculation give best fit with experiments. In this chapter, we also studied the orbital ordering of this molecule from electron momentum distributions and binding energy spectra, and gave an ordering as:4b₂<2a₂<4b₁<6a₁<3b₂<(3b₁, 5a₁, 1a₂)<(2b₂,4a₁)<2b_<3a₁The third chapter introduces the investigation of the electron momentum distributions of CF₂Cl₂ molecule using high-energy-resolution energy-momentum-dispersive spectrometer.