Graduate

Thesis (Ph.D.)--University of California, Berkeley, 1963. / "UC-4 Chemistry" -t.p. "TID-4500 (24th Ed.)" -t.p. Includes bibliographical references (p. 131-133).

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In this thesis, spectroscopic studies of the catalyzed nuclear spin conversion (NSC) of ortho-H2 molecules in solid H2 matrix and the high-resolution Fourier transform infrared (FTIR) absorption spectra of O2 and NO embedded in matrices of para-H2 crystals are presented. For NSC of ortho -H2, the catalyzed conversion rate was found to be diffusion-determined by setting up systematical kinetic studies of solid H2 samples dopant with O2 and NO. The factors affecting diffusion process were discussed; For the high-resolution FTIR of O2 and NO, sharp lines presumable due to rotational structure were observed. Based on the observation, preliminary analysis of the spectrum was discussed for O2 and NO, respectively. / Yan, Lei. / Adviser: Man-Chor Chan. / Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 84-87). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

In an attempt at studying tunneling motions in the solid para -H2, the infrared absorption spectrum of matrix-isolated ammonia molecules (NH3) has been studied using Fourier-transform infrared (FTIR) spectroscopy. The transitions of the ammonia molecule in the v2 fundamental band were observed to exhibit very different pattern compared to those observed in other matrix materials. A preliminary analysis of the observed spectrum was also discussed based on the effect of crystal annealing and nuclear spin conversion of NH3. Transitions have been assigned to ortho and para species of NH3 based on there behavior in the presence of O2. For a more definitive assignment, further experiments will be necessary. / In this thesis, high resolution infrared spectrum of tetrahexacontapole (64-pole)-induced rovibrational W transition of solid parahydrogen (para-H2) was studied in samples containing ∼0.05% of orthohydrogen (ortho-H2) using high resolution near infrared diode laser spectroscopy. The rovibrational W1(0) transition (v =1 ← 0,J = 6 ← 0) has been observed at ∼6441.73 cm-1 with resolved triplet structure. These components were interpreted as the splitting of the M levels in the v = 1, J = 6 state due to crystal field interaction. The corresponding crystal field parameters based on the model of localized exciton in the W1(0) transition were determined. The good agreement of the corresponding parameters between the W1(0) transition and the previous W0(0) transition confirms the localization of the J =6 roton in both v = 0 and 1 states for solid para-H2. In addition, the temperature dependence of the W1(0) transition was studied in the temperature range of 2.7-8.0 K. The observed frequency shift has been ascribed to the change of isotropic intermolecular interactions as a result of molar volume change at different temperature / Song, Yan. / "November 2009." / Source: Dissertation Abstracts International, Volume: 72-01, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 87-93). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Thesis (Ph. D.)--Ohio State University, 1987. / Includes vita. Includes bibliographical references (leaves 208-211). Available online via OhioLINK's ETD Center.

Solid hydrogen forms at extreme conditions, under high pressures. Although the hydrogen atom is easy to understand theoretically, when interacting in the solid state it becomes complicated. Up to now, five different solid phases have been confirmed experimentally and theory has predicted numerous competing crystal candidates. The goal is to obtain solid metallic hydrogen which has been predicted theoretically eighty years ago and has since been considered the holy grail of high pressure science. In nature, this form of matter is believed to exist at the core of large planets like Jupiter and Saturn, being responsible for the planets' large magnetic fields. Understanding the different phases of hydrogen is a test for our most advanced theories of quantum mechanics in condensed matter and it is fundamentally important for both planetary and material science. Recently discovered solid phase IV is stabilized by entropy and therefore only exists at relatively high temperatures. Using molecular dynamics (MD) I studied the room temperature behavior of phase IV starting with the ground state candidate structures reported in the literature. Additionally, I devised a velocity projection method for extracting Raman spectra from MD in light of direct comparison to experiment. My results helped establish the true nature of phase IV and validated the structure against experimental data. Applying the same method to the previously proposed C2=c crystal structure, I obtained results that confirm this structure is the best candidate for phase III. Within the last year, a new phase V of solid hydrogen was discovered in Raman experiments. While attempting to identify the crystal structure associated with this new phase, I discovered a manifestation of solid hydrogen in the form of long polymeric chains that could be stabilized by a charge density wave. Here I discuss the possibility of such a state of matter as an intermediate on the path to molecular dissociation of hydrogen. Chains could, however, be a spurious structure - the effect of a subtle non-convergence problem in the MD, which could indicate serious issues with many previous studies reported in the literature. A far more likely candidate for phase V is a structure similar to that of phase IV with a subtle dynamical modification. I will present Raman and phonon results from both static and dynamic calculations to support this claim. I conclude my work on pure solid hydrogen with an instructive model that could explain the entire phase diagram based on simple thermodynamic considerations. All of the assumptions were extracted from our previous ab initio studies through analysis and observations. This model encodes a comprehensive summary of the current understanding of solid hydrogen at high pressures. Raman and infrared spectroscopy have been the methods of choice in most hydrogen studies. Another way to look at the problem is to analyze the behavior of isotopic mixtures: hydrogen-deuterium binary alloys. Using isotopic substitutions, I revealed a textbook effect in hydrogen: phonon localization by mass disorder. The effect might be unique to this element, owing to the large mass ratio between hydrogen and deuterium. Phonon localization explains the complicated Raman spectra obtained experimentally in hydrogen-deuterium mixtures at various concentrations. More recent experimental results claim an unexpected phase transition in mixtures at low temperatures based on splittings in the infrared spectra. Here I will show that the infrared splitting seen experimentally could be induced by mass disorder in phase III and does not necessarily indicate a structural transformation.

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