| The study of photoionization and photodissociation processes of small molecules in gas phase is an important tool to understand structures of the molecules and corresponding ions and to determine physicochemical parameters such as ionization energies and chemical bonding energies,which can provide important fundamental data for related fields such as interstellar chemistry,atmospheric environment,combustion reactions and plasma etching.Through the combination of photoelectron spectroscopy,mass spectrometry and ion velocity map imaging,we can perfrom stateof-art investigations of molecular and ionic excited states,revealing bond-breaking dynamic processes and fragmentation channels.In this thesis,we have applied the threshold photoelectron-photoion coincidence velocity imaging mass spectrometer,combined with theoretical calculations and spectroscopic simulations,to deeply analyse threshold photoelectron spectra of difluorodichloromethane.As a result,more accurate fundamental data like ionization energy,chemical bonding energy and appearance potential energies for ionic fragments have been obtained with vibrational identification of electronic state transition,and we have also preliminarily explored dissociation mechanisms of electronically excited states of ions.In addition,we have also conducted a preliminary investigation of dissociation dynamics of hydrogen sulphide ions in low electronically excited state using a combination of resonanceenhanced multiphoton ionisation and velocity map imaging.The major results are briefly summarized as follows.(1)Threshold photoelectron spectroscopy and thermodynamic parameter determination of CF2Cl2+ in X2B2 ground state.In this work,we performed threshold photoelectron spectroscopy and density functional theory calculations for CF2Cl2.A global Franck-Condon simulation of the vibrationally resolved threshold photoelectron spectrum of the X2B2 band was carried out at the ωB97XD/cc-pVTZ level using optimised geometries and vibrational frequencies of CF2Cl2 neutral and corresponding ion both in ground state.Based on the excellent agreement between the experimental and simulated spectra,we identified most vibrational peaks,and obtained an accurate adiabatic ionization energy(AIE)of 11.590±0.010 eV.Then,the formation enthalpy of CF2Cl2 neutral and ions,as well as the C-Cl bond energies,were determined.(2)Threshold photoelectron spectroscopy and dissociation dynamicss of CF2Cl2+in low-lying excited state.For CF2Cl2+in low-lying electronically excited states,we calculated optimized geometries and vibrational frequencies of the B2B1,C2A1 and D2B2 excited states,respectively,at the ωB97XD/aug-cc-pVTZ level.Based on the Franck-Condon simulation,we reattributed the vibrational peaks of photoelectronic spectrum of the B2B1 band and obtained its accurate AIE of 13.120±0.005 eV,as well as three symmetric vibrational frequencies of v1+=1170 cm-1,v2+=645 cm-1 and v4+=242 cm-1,respectively.Similarly,we obtained an AIE of 13.300±0.015 eV for the C2Ai ionic state and 14.125 ± 0.005 eV for the D2B2 state and corresponding vibrational frequencies,v1+=1178 cm-1 and V3+=361 cm-1.In addition,we recorded the ion velocity map images of the CF2C1+fragment in dissociativephotoionization process via different ionic excited states.Additionally,we also performed quantum chemical calculations for the C-Cl bond breaking potential energy curves,and a preliminary discussion of the Cl-loss dissociation mechanism of CF2Cl2+was presented.(3)Preliminary study of the dissociation dynamics of H2S+in the A2Ai state with high vibrational excitation.In this work,we prepared H2S+ions in ground state without vibrational excitation by(2+1)resonance-enhanced multiphoton ionisation(REMPI),and detected the S+and SH+fragment ions dissociated from its A2Ai state produced by photoexcitation with a second laser.Thus,the photofragment excitation spectra of S+ in a specific wavelength range were recorded,providing a preliminary study for further ion velocity map imaging measurements. |
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