2026-09-21T02:35:34Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/466462022-01-13T07:54:21Zcom_1721.1_7582com_1721.1_7581col_1721.1_131022
Robert W. Field.
Bittinger, Kyle Lee
Massachusetts Institute of Technology. Dept. of Chemistry.
Massachusetts Institute of Technology. Department of Chemistry
2009-08-26T17:11:42Z
2009-08-26T17:11:42Z
2009
2009
http://hdl.handle.net/1721.1/46646
426898604
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009.
Vita.
Includes bibliographical references (p. 229-239).
Intersystem crossing in acetylene, C₂H₂, is described by a doorway-mediated model, where singlet-triplet mixing between the first excited singlet~ state, S₁, and the manifold of low-lying T₁,₂ states is controlled by special vibrational levels of the third excited triplet state, T₃. However, the influence of T₃ doorway states on the ~A¹Au <-- ~X¹[sigma]+g spectrum of acetylene is not well characterized for most S₁ vibrational levels. The doorway model is formulated to account for the LIF/SEELEM spectra of S₁ vibrational sublevels that are weakly perturbed by T₃ doorway states. The structure and properties of a doorway-mediated effective Hamiltonian are discussed, and a method for spectral deconvolution is presented for the doorway model. The dependence of fluorescence center-of-gravity on the time delay of a gated integration region is developed as an analysis tool for LIF spectroscopy. Triplet perturbations in the spectra of four S₁ vibrational sublevels are discussed in terms of the doorway model, using this new tool. IR-UV double resonance LIF/SEELEM spectroscopy is used to investigate the role of the torsional and "cis"-bending vibrational modes of S₁ in the promotion of vibrational overlap between levels of S₁ and T₃. A collisional method for the population of metastable molecules in a pulsed supersonic expansion is presented and discussed.
by Kyle Lee Bittinger.
Ph.D.
240 p.
eng
Massachusetts Institute of Technology
M.I.T. theses are protected by
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http://dspace.mit.edu/handle/1721.1/7582
Chemistry.
Spectroscopic signatures of doorway-mediated intersystem crossing
Thesis
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<Abstract>Intersystem crossing in acetylene, C₂H₂, is described by a doorway-mediated model, where singlet-triplet mixing between the first excited singlet~ state, S₁, and the manifold of low-lying T₁,₂ states is controlled by special vibrational levels of the third excited triplet state, T₃. However, the influence of T₃ doorway states on the ~A¹Au <-- ~X¹[sigma]+g spectrum of acetylene is not well characterized for most S₁ vibrational levels. The doorway model is formulated to account for the LIF/SEELEM spectra of S₁ vibrational sublevels that are weakly perturbed by T₃ doorway states. The structure and properties of a doorway-mediated effective Hamiltonian are discussed, and a method for spectral deconvolution is presented for the doorway model. The dependence of fluorescence center-of-gravity on the time delay of a gated integration region is developed as an analysis tool for LIF spectroscopy. Triplet perturbations in the spectra of four S₁ vibrational sublevels are discussed in terms of the doorway model, using this new tool. IR-UV double resonance LIF/SEELEM spectroscopy is used to investigate the role of the torsional and "cis"-bending vibrational modes of S₁ in the promotion of vibrational overlap between levels of S₁ and T₃. A collisional method for the population of metastable molecules in a pulsed supersonic expansion is presented and discussed.</Abstract>
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