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Lutz Hüwel






Three different research projects were performed and documented in this dissertation. With the help of a molecular beam, a linear time-of-flight (TOF) spectrometer, and a pulsed laser system, experiments were performed that led to (i) understanding of the different pathways of Na+ production in a non-resonant multi-photon ionization using 355 nm and 532 nm photons, (ii) measurement of vibrational lifetime dependence of the 21Su+ and 41Sg+ states, and (iii) the study of the shallow well of the Na2+ 12Σu+ state.

In the non-resonant multi-photon ionization project, flight time spectra reveal several processes with Na+ photo-fragment energies ranging from 0 to 1.32 eV. Emphasis lies on 2(or 3)-photon excitation followed by dissociative autoionization along doubly excited states converging to the repulsive 12Σu+ state of Na2+. A semi-classical model is employed to explain the observed fragment energy distribution in this process which involves competition between electronic (autoionizing) and nuclear (dissociative) degrees of freedom. A fit to experimental polarization dependent TOF spectra was accomplished using model Rydberg potential curves with position dependent autoionization widths Γ(R) and appropriate fragment angular distributions.

The second project is about lifetime measurements of the 21Su+ and 41Sg+ states. With the aid of high resolution dye lasers used for excitation and using variable delay pump-probe resonant ionization technique, the radiative lifetime of the selective individual vibrational levels of the 21Σu+ state (v = 22 – 52) and of the 41Σg+ state (v = 43 – 65) of Na2 have been experimentally measured as a function of vibrational quantum number. Calculation of lifetimes was also performed using the Level 8.0 and BCONT programs. In general, it has been observed in both experiment and calculation that a strong variation of lifetime exists especially as the vibrational levels approach the potential barrier of the 21Σu+ stateor the shelf of the 41Σg+ state. Overall lifetime magnitude measured and calculated for the 21Σu+ stateis in good agreement with the vibrationally averaged lifetime data reported by Mehdizadeh. For the 41Σg+ state, the current work is the first account of lifetime data. Again, the overall experimental lifetime trend agrees with the calculation.

The third project relies on Zero Electron Kinetic Energy (ZEKE) technique. Experiments using ZEKE was successfully demonstrated in the laboratory for the 12Σg+ state of the Na2+. Two rotational levels were successfully identified for v = 0 of the ground ion state. However, the attempt of this study to measure experimentally the ro-vibrational levels and spacing of the 12Σu+ state of Na2+ was unsuccessful. Calculations using LEVEL 8.0, the program used for calculating the bound vibrational levels of a diatomic molecular potential was tested and the shallow well of the 12Σu+ state with a depth of about 70 cm-1 was predicted to have about 26 bound vibrational levels.



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