Browsing by Author "Kinsey, James L."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Continuously-scanned Raman excitation profiles for ozone excited in the Hartley band
    (2000) Hsiao, Chih-Wei; Kinsey, James L.
    Improvements in the determination of the continuously-scanned Raman excitation profiles (REP's) are described. The continuous-scanning technique is applied to ozone excited in the first continuum (the Hartley band). The Rayleigh excitation profile, which is required for intensity calibration, is obtained simultaneously. A theoretical calculation for the ozone Rayleigh excitation profile is also provided for comparison. REP measurements of the vibrational features up to 6 quanta are determined in the wavelength range of 238--271 nm. These spectra show oscillatory structures that are qualitatively but unambiguously identified as the Raman counterparts of those in the absorption spectrum. The use of overlapping dye mixtures to cover most of the Hartley band is required. Difficulties encountered in patching together these first-generation spectra are discussed in detail.
  • Thumbnail Image
    Item
    Photodissociation dynamics of ozone using Raman excitation profiles (REP's)
    (2005) Lotfi, Erik Siavash; Kinsey, James L.
    Because of the environmental importance, ozone has long been one of the prominent research topics in the scientific community. Surprisingly, in spite of all the research, the UV photodissociation dynamics of ozone has not been completely understood yet. More specifically, the origin of the small structural features overlapping the broad-band feature in the UV absorption spectrum of ozone still remains a mystery. However, theoretical calculations done in our lab predict, subject to UV radiation, great majority of ozone molecules fall apart in roughly 6 femtoseconds while a very minute portion, about 1% corresponding to small structural features take much longer to dissociate (up to 150 femtoseconds). Even with the fastest lasers currently available, it would not be possible to learn about the photodissociation dynamics of ozone using Femtosecond chemistry. However, a unique technique called continuous-scan Raman Excitation Profiles developed and tested on iodobenzene in our lab has proven to be a powerful method in learning about extremely fast dissociating processes such as ozone. One of the features that make REP's a powerful tool is that, it provides valuable knowledge of time domain behavior based on only the intensity and frequency of the emitted photons. However, primarily because of its extremely low photon yield, one must overcome several significant and challenging experimental problems associated with the apparatus before achieving any reliable ozone REPs. The main objective of this thesis is to demonstrate how these problems were solved and to discuss and analyze some recently obtained preliminary data to be the guide for those pursuing full-scale ozone REP'S in the future.
  • Thumbnail Image
    Item
    Raman spectroscopy of photodissociating molecules
    (1995) Stevens, Richard Eric; Kinsey, James L.
    Dissociative Resonance Raman Spectroscopy has been used to probe the dissociation dynamics of two different molecules, dimethyl zinc and methyl mercaptan. A method for analytically describing potential energy surfaces by the use of rational approximants is described. A rigorous, systematic algorithm to remove spurious singularites from such approximants is presented. A tunable, narrow band UV laser system has been developed capable of generating 10 nsec pulses of 10 mJ energy, with a bandwidth of less than 1 $\rm cm\sp{-1}.$ The tuning range of the ArF final amplifier is 192 to 194 nm, and use of a stimulated Raman scattering cell allows for tuning up to 205 nm at 0.5 mJ energy per pulse. The Raman spectrum of DMZ is complicated by the appearance of Zn atom and ion lines. The fundamental and 1st overtone of a methyl umbrella mode are the only Raman features seen. The Raman spectrum of methyl mercaptan shows a progression which we assign to the C-S stretching mode. A strong feature we assign to the S-H stretching fundamental exhibited no overtones. Our results show that a previous assignment from a low resolution spectrum taken in another laboratory is erroneous. Methyl mercaptan's Raman spectrum is complicated by the appearance of CS fluorescence and atomic carbon fluorescence. A pathway is proposed for the multi-photon formation of these emitting species at 193 nm.
  • Thumbnail Image
    Item
    The resonance Raman spectroscopy of nitrosyl chloride in the A-band
    (2000) Mackey, Jeffrey Laurence; Kinsey, James L.
    The resonance Raman spectrum of nitrosyl chloride (CINO) has been measured using excitation wavelengths of 212.5, 219, and 222 nm. These spectra add twelve new vibrational energy levels to the previously-known sixteen levels. A ground state potential energy surface was determined, using a Jacobi coordinate system, resulting in converged energies and wavefunctions for all measured vibrational levels. The resonance Raman spectrum of nitrosyl chloride is interpreted in terms of the dynamics on the electronically-excited potential energy surface. Progress toward a novel scheme for solving the time-dependent Schrodinger equation for the vibrational degrees of freedom of the molecule using a multiwavelet basis set is discussed.