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UV Photodissociation Dynamics of Polyatomic Free Radicals Using High-n Rydberg Atom Time of Flight Spectroscopy

  • Author(s): Lucas, Michael
  • Advisor(s): Zhang, Jingsong
  • et al.
Abstract

The ultraviolet (UV) photodissociation dynamics of several free radicals were studied using High-n Rydberg H-atom time-of-flight (HRTOF) spectroscopy, including the nitrogen contain aromatic radicals o-pyridyl and m-pyridyl, cyclohexyl which is a cyclic alkyl radical, and four isomers of the unsaturated C4H7 radical system. The four isomer studied where 1-methylallyl, 2-methylallyl, 2-buten-2-yl, and 2-methyl-1-propenyl radicals. The vacuum ultraviolet (VUV) photodissociation dynamics of methanol was also studied.

The first chapter discusses photodissociation dynamics as well as the experimental methodology. The HRTOF experimental technique used in this research is explained in detail.

The second chapter investigates the UV photodissociation of o-pyridyl radicals in the region of 224-246 nm. The H-atom product translational energy release indicates the production of cyanovinylacetylene + H. The H-atom product yield spectrum, product angular distribution and photodissociation mechanism were also obtained.

Chapter 3 investigates the UV photodissociation of m-pyridyl radicals in the region of 224-246 nm. The H-atom product translational energy release distribution indicates the production of cyanovinylacetylene + H. The H-atom product yield spectrum, product angular distribution and photodissociation mechanism were also obtained.

Chapter 4 investigates the UV photodissociation of cyclohexyl radicals in the region of 232-262 nm. The H-atom photofragment yield spectrum is in good agreement with previously reported UV absorption spectra. The production translation energy release distribution indicates a non-statistical photodissociation process to produce cyclohexene + H. The product angular distribution showed an anisotropic distribution. The photodissociation mechanism was obtained.

Chapter 5 investigates the UV photodissociation of the 1-methylallyl, 2-methylallyl, 2-buten-2-yl, and 2-methyl-1-propenyl radicals. The H-atom time-of-flight spectra of three of the four C4H7 radicals showed a bimodal feature indicating two photodissociation mechanisms while the 2-methyl-1-propenyl radical showed a single feature. All of the isomers showed a statistical H-atom product channel while 1-methylallyl, 2-methylallyl, and 2-buten-2-yl also showed a non-statistical photodissociation H-atom product channel. The H + C4H6 product translational energy distributions and the photodissociation mechanism were obtain for each of the radicals.

Chapter 6 discusses the VUV photodissociation of CH3OH and CH3OD at 121.6 nm. The H-atom product TOF spectrum of CH3OH and D-atom spectrum have a bimodal distribution. The photodissociation mechanisms and branching ratios were obtained.

Chapter 7 will briefly discuss the results of a related system, 3-cyclohexenyl radical, and general conclusions.

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