Ion-Pair Photodissociation Dynamics Study Of CCl₃H, CF₂Cl₂ And CFCl₃ Using Synchrotron Radiation

Ion-pair photodissociation, established as a novel unimolecular process, occurs rather commonly in a wide energy range of several to hundreds eV and for various molecules from diatomic molecules to the complicated polyatomic molecules. Vacuum ultraviolet synchrotron radiation is a suitable photon source for the ion-pair dissociation studies, owing to the distinguished merits of synchrotron radiation such as the high brilliance and tunnability in a wide range of photon energy. We carried out a series of photodissociation studies on CCl₃H (chloroform), dichloro- difluoromethane (CF₂Cl₂) and trichloromonofluoromethane (CFCl₃) using synchrotron radiation at the atomic and molecular physics end-station of National Synchrotron Radiation Laboratry at Hefei, China.This dissertation is consisted of five chapters.In the first chapter, the basic physics of the photon-molecule reactions, especially of ion-pair photodissociations, and the experimental and theoretical methods used are introduced briefly.The second chapter is the intoduction of the ion-pair photodissociation method using synchrotron radiation. To record the ion-pair anion production efficiency curves, the mass spectrometer was successfully modified. Moreover, we've developed the threshold ion pair production spectroscopy (TIPPS) on the basis of the mass analyzed threshold ionization (MATI). The final design drawings are presented after a lot of simulation work and calculations.The third chapter is the ion-pair dissociation dynamics study of molecule CHCl3. Negative ions and their isotope species are observed for the first time in the photoexcitations of CCl3H in the energy range of 10.0-21.5 eV and tentatively assigned according to literatures.The spectra of two isotopes ³⁵Cl^ˉand ³⁷Cl^ˉshow some additional peaks due to the energetically accessible multi-body fragmentations. A distinct peak at 14.55 eV may be owing to a cascade process. Two vibrational excitation progressions, nν2⁺ and nν2⁺+ν3⁺, nν4⁺ and nν4⁺+ν2⁺, are observed around C2E and D 2E ionization states, respectively.The forth chapter is the ion-pair dissociation dynamics study of molecule CF₂Cl₂. Negative ions 35Cl^ˉ, 37Cl^ˉ, and F^ˉare observed in the VUV photo-dissociations of CF₂Cl₂ using synchrotron radiation and their ion production efficiency curves are recorded in the wide photon energy range of 8.00― 20.50 eV. The fragmentation enthalpies are estimated on the basis of the high-level G3MP2 calculations performed in this work. The Cl^ˉproduction curve is recorded below the first ionization threshold and assigned. The energetic threshold for CF₂Cl₂ + hν→Cl^ˉ+ CF₂Cl+ is determined to be 8.20±0.04 eV. The F^ˉanionic fragment is observed in the energy range of 17.30– 20.50 eV, and we find a novel competition between the ion-pair photodissociations to Cl^ˉand F^ˉ. A series of Rydberg transitions together the multi-body fragmentation channels are tentatively assigned in the spectra of Cl^ˉand F^ˉin this energy range.The fifth chapter is the ion-pair dissociation dynamics study of molecule CFCl3. Anionic fragments, F^ˉand Cl^ˉ(two isotope species 35Cl^ˉand 37Cl^ˉ), are observed. The ion-pair anion efficiency spectra of 35Cl^ˉand 37Cl^ˉare recorded in the photon energy range of 7.75― 22.00 eV. The threshold of ion-pair dissociation CFCl3→CFCl2+ + Cl^ˉis experimentally determined to be 7.94±0.04 eV. With the references of the high-resolution photoabsorption spectra, the electron transitions from the valence to Rydberg orbitals are assigned in the Cl^ˉefficiency spectrum. The multi-body ion-pair fragmentation processes to produce Cl^ˉare discussed in this text.The conclusions and the research plans in future are given at the last of this thesis.