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State-resolved photochemistry and spectroscopic characterization of atmospherically relevant hydroperoxides


This dissertation focuses on the photodissociation dynamics, thermochemistry, spectroscopy and structure of important hydroperoxide molecules which influence the oxidation capacity of the atmosphere. Since hydroperoxides such as CH₃OOH, HOCH₂OOH, HO₂NO₂ and HOOH species serve as reservoir for the HOx (=HO₂ + OH) radicals, a thorough examination of excited state and ground state photochemistry of these species is needed. In this dissertation, the photodissociation dynamics of vibrationally excited HO₂NO₂ molecule is examined, and its first OH-stretching state dissociation quantum yield is assessed in order to quantify its contribution to the HOx budget. An ab initio study is used to obtain bond dissociation energies, vibrational spectra and absorption cross-sections. The HOONO molecule is an important structural isomer of nitric acid. Studies of HOONO molecule have primarily focused on the vibrational structure, spectra and energetics of vibrational states in the vicinity of the first and second OH-stretching overtones. From these measurements, the heat of formation and vibrational band assignment of cis-cis HOONO are determined. Organic hydroperoxides such as CH₃OOH and HOCH₂OOH are fundamental systems to explore the flow of energy among different vibrational modes. In HOCH₂OOH, the dissociation rates that are extracted from the third OH- stretching overtone suggest that excitation of the alcohol OH-stretch result in dissociation rates that are substantially slower than rates resulting from excitation of the peroxide OH-stretch where IVR is evidently more restricted. Non-statistical behavior is also observed in CH₃OOH, where the excitation of HOO-bending mode and CH- stretching modes result in more complete IVR due to strong state-mixing compared with excitation of the OH-stretching modes; as inferred from the quantities of vibrationally excited OH product formed. Enhanced IVR mixing is also observed in HOOH molecule, suggesting mode-selective behavior is a common occurrence in hydroperoxide molecules. Lastly, rotational band analysis of jet-cooled CH₃OOH facilitates band assignment and structure of the first and second OH-stretching overtones and their corresponding torsional states. The analysis also shows that interactions between the bright OH-state and dark background states lead to inhomogeneous line broadening and band perturbations. These interactions predominantly arise from interaction between the symmetric HOOC-torsion/ OH-stretching states and the CH-states of the methyl rotor

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