Experimental And Theoretical Studies On Single And Double Photoionization Of Small Molecules

The dissertation mainly introduces the experimental and theoretical studies on single and double photonization of small molecules by using tunable VUV synchrotron radiation.It also introduces the development,installation and adjustment of gas filter system of atomic and molecular physics beamline at National Synchrotron Radiation Laboratory.In the first chapter,it introduces the present status of investigation on photoionization and photoabsorption of atoms and molecules.The basic conceptions of photoionization and photodissociation,such as adiabatic ionization energy,vertical ionization energy,superexcited states,Rydberg states,photoionization cross section, photoabsorption cross section,photodissociation,predissociation,and so on,are discussed in details.Then,the common experimental method,including photoionization mass spectrometry,photoabsorption spectrometry,fluorescence spectrum,photoelectron spectrum,threshold photoelectron spectrum and some coincidence technologies,are also introduced.Finally,the theoretical calculation methods are also described in detail,In the second chapter,first,it summarizes the development,characteristics and applications of synchrotron radiation.Secondly,it introduces the structure and equipments of atomic and molecular physics beamline and endstation at National Synchrotron Radiation Laboratory.The undulator can provide the tunable VUV synchrotron radiation in the energy range of 7.5-124 eV.Finally,the formation mechanism of ultrasonic molecular beam,principle of time of flight mass spectrometer and multi-photonization photoabsorption chamber are discussed in details.In the third chapter,a differentially pumped rare gas cell has been developed to suppress high order harmonics on the atomic and molecule physics beamline at National Synchrotron Radiation Laboratory.The gas filter system contains a gas absorption cell and two differential pumping systems in consideration of the present status of atomic and molecule physics beamline.The adjustment results indicats that when the pressure of Ar in the gas absorption cell is set to 9.31 Torr,the filter factor of gas filter system is better than 99.975%.Generally speaking,the adjustment results of the gas filter system are in agreement with the design parameters and can meet the experimental requirement very well.In the fourth chapter,Photoabsorption spectra of CO are investigated in energy region 630-900(?) by using synchrotron radiation.Rydberg series converging to the X²âˆ‘,A²âˆand B²âˆ‘states of CO⁺ are identified,and the quantum detect values are also calculated.By analysis and comparison,our results are accurate and credible.Besides Rydberg series and vibrational progressions are extended,some new Rydberg series are also identified clearly.In the fifth chapter,the ionization energy of CO and appearance energies for its fragment ions(C⁺,O⁺),are determined with photoionization efficiency spectroscopy. The total energies of CO molecule and all fragment products are calculated using Gaussian 03 program and Gaussian 2 calculations.And then,the adiabatic double ionization energy of CO molecule,appearance potentials for its fragment ions and dissociation energies to produce them are predicated by using high accuracy energy mode.The experimental ionization energy and appearance potentials are all in reasonable agreement with their respective calculated energies.The states of fragments are identified in the dissociative course.The mechanisms of photoionization,predissociation and photodissociation of CO are discussed based on comparison of our experimental results with those predicted theoretically.In the sixth chapter,VUV double photoionizations of small molecules(NO,CO, CO₂,CS₂,OSC and NH₃) are investigated with photoionization mass spectroscopy using synchrotron radiation.The double ionization energies of molecules are determined with photoionization efficiency spectroscopy.The total energies of these molecules and their parent dications(NO²⁺,CO²⁺,CO₂²⁺,CS₂²⁺,OSC²⁺ and NH₃²⁺) are calculated using Gaussian 03 program and Gaussian 2 calculations.And then,the adiabatic double ionization energies of molecules are predicated by using high accuracy energy mode.The experimental double ionization energies of these small molecules are all in reasonable agreement with their respective calculated adiabatic double ionization energies.The mechanisms of double photoionization of these molecules are discussed based on comparison of our experimental results with those predicted theoretically.The equilibrium geometries and harmonic vibrational frequencies of molecules and their parent dications are calculated by using MP2(full) method.The differences of configurations between these molecules and their parent dications are also discussed on the basis of theoretical calculations.In the seventh chapter,VUV double photoionization of CHF₂Cl in an energy region 32-40 eV is investigated with photoionization mass spectroscopy by using synchrotron radiation.The double ionization energy of CHF₂Cl and appearance energies for its main fragment dications(CHCl²⁺,CF₂²⁺ and CHFCl²⁺),are determined with photoionization efficiency spectroscopy for the first time.The single point energies of CHF₂Cl and its parent dication(CHF₂Cl²⁺) are calculated using Gaussian 03 program and density functional theory(DFT,B3LYP functional).The vertical double ionization energy of CHF₂Cl is predicted by using B3LYP method and empirical equation.According to our research results,the experimental double ionization energy of CHF₂Cl is in good agreement with the theoretically calculated vertical double ionization energy.The mechanism of double photoionization of CHF₂Cl is discussed based on the comparison of our experimental results with those predicted theoretically.