Laser excited fluorescence and vibrational relaxation of matrix isolated metal oxides Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/df65vc36k

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  • The work presented in this thesis deals with the mechanisms by which a vibrationally excited diatomic molecule gives up its energy to a host monatomic lattice at low temperature. The vibrational lifetimes (v"=1) of the metal oxides Ba0 and A10 in their ground electronic states are studied using pulsed dual laser techniques. Chapter 1 provides a brief-overview of the theoretical and experimental details relating to the field of vibrational relaxation in matrices. In Chapter 2, laser excited fluorescence spectra are presented for Ba0 prepared by VUV photolysis of Ar/Ba/0₂ matrix samples at 18 K. Evidence was obtained for a new Ba0 electronic state with T [subscript e] =20,000 cm ⁻¹ and a radiative lifetime shorter than 15 Optical-optical double-resonance studies were not successful due to the low pumping efficiency and/or rapid vibrational relaxation. An infrared study of the aluminum oxide products formed by rapid condensation of gas phase Ar/0₂/A1 mixtures is presented in Chapter 3. By coupling a double-resonance infrared-visible pump/probe scheme, the 0[arrow]1 transition of A10 in argon was positively identified at 974.9 cm⁻¹ for Al ¹⁶0 and at 942.4 cm ⁻¹ for A1¹⁸0. Laser excited fluorescence and visible absorption spectra are presented for A10 in argon at 18 K. Vibrational relaxation studies of A10 are described in Chapter 4. The 0=1 lifetime is independent of oxygen concentration and of temperature in the region between 18 and 30 K. An upper limit of 25 ms. is measured for dilute matrices with less than one PPM A10. At higher concentrations of Al and other oxides, this lifetime is shortened considerably by V-V transfer of vibrational energy to molecular impurities. A quantitative study of the V-V transfer process from A10 to both polar (NH₃, ND₃, CH₂C1₂) and non-polar (SF₆, C₂H₄, C₂H₆, CO₂, and CF₄) acceptors is the subject of Chapter 5. The transfer rate coefficients show an exponential dependence on the donor-acceptor energy gap, decreasing approximately one order of magnitude for each lattice phonon needed to take up the excess energy. A mechanism which assumes that the energy mismatch between donor and acceptor is directly transferred to the lattice is most consistent with the observed data.
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