A Number Of Molecular Resonant Multiphoton Ionization And Multiphoton Ionization Dissociation Kinetic Studies

1. A brief introduction is given on molecular multiphoton ionization - time of flight (MPI-TOF). It includes the history and new development of multiphoton ionization, some characteristics of multiphoton process, multiphoton ionization spectra (MPI Spectra), multiphoton ionization - photoeletron spectroscopy (MPI-PES), multiphoton ionization - dossociation mass spectroscopy (MPID-MS).2. Chapter 2 describe the experimental setup in detail, including laser source, molecular beam and vacuum system, TOF mass spectrometry, and ionic detector.3. In chapter 3, laser power index in multiphoton processes is carefully analyzed for the simple three-energy system. The result shows that the absorption cross section can be estimated with the laser intensities in the changing region of absorption saturation. The validity of our method is demonstrated by means of some numerical and experimental results.4. In chapter 4, we find the laser power index decreases when reducing the aperture of diaphragm. Numerical calculation shows that the laser beam's temporal structure and spatial structure in the lower laser power region have very little effect on laser power index, but the laser beam's spatial structure exerts very large influence on multiphoton ionization processes in the higher laser power range. Our analysis can explain the experimental results.5. In chapter 5, the mass-selected MPI spectra and time of flight mass spectra of acetone in 61000 65900cm^-1 were obtained using multiphoton ionization time-of-flight mass spectrometric technique. Mass-selected MPI spectra of these main cations exhibited the same feature, could be attributed to (no,3d) mixed Rydberg-valence and (no,4s) Rydberg transitions. Two relative strong ion peaks were assigned to CH₃CO⁺ and CH₃⁺, and weak ion peaks to C⁺, CH⁺, CH₂⁺, CHO⁺, no parent ion peak was observed in the wavelength region. We also measured the dependence of fragmental ratio of each ions on laser intensity and laser power index of total ions. Based on our experimental results, the multiphoton ionization-dissociation (MPID) mechanics of acetone was discussed. The MPID of parent laddering switch model was analyzed withrate equation. Using simple three-energy system model, we also estimated three photon absorption cross sections of no -> 3d and no->4s transition.6. (1) The time of flight mass spectra of acetone and propanal at 532nm were obtained using multiphoton ionization time-of-flight mass spectrometric technique. We also measured the percentage of fragment ions to the total ion current, and the dependence on laser intensity of the two molecules. Based on our experimental results, the multiphoton ionization-dissociation (MPID) mechanics of acetone and propanal were discussed. Some channels of the small fragment cations, i.e. H+, C+, CH+, and CH2+, etc. were also analyzed. (2) The resonant-enhanced multiphoton ionization (REMPI) spectra and mass spectra of triethylamine (TEA) molecule were obtained in the wavelength range of 445.9 465.9nm with a pulsed dye laser. The laser intensity and pressure dependence of the two ions were measured. Based on our experimental results, the possible Multiphoton Ionization-Dissociation process of TEA molecule in the wavelength region was discussed in detail.7. The mass-selected MPI spectra and time of flight mass spectra of 2-butanone in 467.1 488. lnm were obtained using multiphoton ionization time-of-flight mass spectrometric technique and dye laser. Two relative strong ion peaks were assigned to C2H3O"1" and C2H5"1", and weak ion peaks assigned to C2H2+, C2H3+ and CH3"1", no parent ion peak and CHsCFkCO* were observed in the wavelength region. Mass-selected REMPI spectra of the main cations exhibited the same feature, four peaks coincided well with VUV absorption spectra, but the relative intensity of the MPI spectra peaks is strongly different from that of VUV absorption spectra. Based on our analysis, the strongest MPI spectra peak could be attributed to (no, 3d) Rydberg transitions, and the spectra in 63591 63897cm"1 is mixed Rydberg-valence vibronic transitons. We also measured the laser power index of the fragmental and total ions, three photon absorption cross section of (no, 3d) transition of 2-butanone was estimated to be 1.2 X 10"8Ocm6s2 with the total ions laser power indexes. Based on our experimental results, the multiphoton ionization-dissociation (MPID) mechanics of 2-butanone was discussed.8. In the chapter, We describe the work on reducing the shakes between laser pulse and external triggering signal.