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Spectroscopy Studies of Free Radicals and Ions Containing Large Amplitude Motions

Huang, Meng
http://rave.ohiolink.edu/etdc/view?acc_num=osu1515012236254284

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Chemical Physics.
Molecular vibrations can be understood by means of spectroscopy, which involves measuring the light a molecule can absorb or emit as the vibrational energy changes. Large amplitude motions are molecular vibrations which have large atomic displacements. The harmonic oscillator, which is the basic model for small-amplitude molecular vibrations can fail in describing these large-amplitude motions. My dissertation research is mainly focused on developing theoretical models to understand the spectra of molecules that contain large-amplitude motions. One of the interesting questions related to large-amplitude motions is how the large-amplitude displacements affect the frequencies of small-amplitude vibrations in the molecule. A reduce dimension model is built for systems that contain a methyl (CH3) rotor in which the large-amplitude methyl torsion is coupled to the small-amplitude CH stretches. This model was applied to two systems, methyl peroxy radical (CH3OO) and methanol radical cation (CH3OH+). In methyl peroxy, the coupling between CH stretch and methyl torsion is small, which leads to the broadening of features related to the rotational structure when a CH stretch is excited. In methanol cation, this coupling is large and leads to excitations of the torsion and the CH stretches. Good agreement between the experiment and simulations in both systems demonstrate that my model is appropriate to describe the coupling between CH stretch, molecular rotation, and methyl torsion in these systems. Another focus of research in this dissertation is the identification of the carrier of the electronic spectrum observed following the photolysis of CH2I2 in the presence of O2. A one-dimensional model for the large-amplitude CH2X torsion is used to calculate the vibrational bands in the electronic spectrum. The carrier of the spectrum is determined to be based on CH2IO2 radical based on the good agreement between the measured spectrum and the simulation with parameters derived for CH2IO2 radical. Other than the methyl rotor systems, a similar model is also applied on water-halide cluster I-(H2O), where the in-plane bend is a large-amplitude motion. With considering the couplings between the in-plane bend and the OH stretches as well as the couplings between the in-plane bend and molecular rotations, the rotational contour simulations reproduce the spectral feature in the experimental spectrum. Through these studies, we are able to develop models to allow us to interpret spectra based on fundamental ideas of quantum mechanics.
Terry Miller (Advisor)
Anne McCoy (Advisor)
Igor Adamovich (Committee Member)
200 p.
Physical Chemistry
Molecular Spectroscopy; Chemical Physics; Molecular Vibrations; Ions; Radicals

Recommended Citations

Citations

  • Huang, M. (2018). Spectroscopy Studies of Free Radicals and Ions Containing Large Amplitude Motions [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515012236254284

    APA Style (7th edition)

  • Huang, Meng. Spectroscopy Studies of Free Radicals and Ions Containing Large Amplitude Motions. 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1515012236254284.

    MLA Style (8th edition)

  • Huang, Meng. "Spectroscopy Studies of Free Radicals and Ions Containing Large Amplitude Motions." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515012236254284

    Chicago Manual of Style (17th edition)

osu1515012236254284
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This open access ETD is published by The Ohio State University and OhioLINK.