@Marburg, Universit́e, Diss., 2004--Toulouse.

No description available.

The problem with which this investigation is concerned is that of measuring the rate coefficients for termolecular charge transfer reactions of He2+ in atmospheric pressure afterglows with the minority reacting species. Of particular interest was the discovery that the presence of a third body can change an improbable charge transfer reaction involving He+2 into a very probable one, as in the case of the reaction with argon. For example, in Tables II and II it was shown that less than a 300 torr pressure of helium was required to double the effective rate of reaction of argon with He2+ while over 3000 torr was required for CH4. The sensitivity of the method has been sufficient to detect termolecular components as small as 2 x 10-30 cm /sec and values were found to range widely from 2 x 10 for Ne to 67 x 10-30 cm6/sec for CO2. The size of these termolecular rates not only served to explain specific anomalous efficiencies of the charge transfer process observed in atmospheric pressure lasers but also suggested the general importance of three-body ion-molecule reactions in higher pressure plasmas.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

No description available.

The research described in this dissertation conclusively demonstrates the superior qualitative and quantitative performance of spectroscopic systems which employ a new class of optical detectors--charge transfer device (CTD) detectors. An overview of the operation and characteristics of these detectors, as well as theoretical models predicting their performance are presented. The evaluation of a unique prototype single element CID detector, a commercially available linear CCD detector, and a prototype two-dimensional CCD detector are described. Outstanding characteristics include the ability of the single element CID to quantitate photon fluxes ranging over eleven orders of magnitude, a quantum efficiency of the linear CCD in excess of 90%, and a read noise of the two-dimensional CCD of under 5 electrons. In addition, the use of the linear CCD for molecular fluorescence spectroscopy is demonstrated. A direct comparison of CCD and CID detection for atomic emission spectroscopy using a custom echelle system is described. The second part of these investigations focus on the design of spectrometers compatible with the format of these multichannel detectors. While a large number of spectrometer designs exist, the spectrometer and detector combination which produces the highest possible signal-to-noise ratio (SNR) spectra for a given experimental system is almost always desired. The investigations into optimum spectrometer design have led to the use of a unique spatial interferometer system. The performance of a common path interferometer using a linear charge-coupled device detectors is presented and compared to conventional dispersive systems. The throughput, resolution, and other practical factors are discussed. The common path system has a much larger light gathering ability compared to dispersive systems; however, spatial interferometry suffers from the multiplex disadvantages encountered with other forms of UV/Vis interferometry. A unique crossed interferometric dispersive arrangement allows the simultaneous acquisition of the spectral information while greatly reducing these multiplex disadvantages. Preliminary work on the crossed interferometric system is presented demonstrating significant reduction of these multiplex disadvantages.

Typescript. / Digitized by Kansas Correctional Industries

In large molecular systems such as DNA, supramolecular complexes and dendrimers, functional groups located at different parts of the molecular structure can act as charge donors or acceptors, and photoinduced intramolecular charge transfer can occur. An analogous scenario can be found in colloidal semiconductor nanocrystals, most evident in type-II heterostructures, where the relative band-alignment of the constituent materials are in a stagger configuration. Such a configuration, provides an energetically favourable situation for an photo-generated electron to be transferred from one material to the other, confining the electron and the hole in different domains of the nanostructure. A less obvious scenario in nanocrystals is when the core is thought of as the donor group, and the surface as the acceptor group. In such a scenario, the localization of electron or hole at surface defect sites, a process that occurs in every nanocrystal, can be thought of as an ``intramolecular" charge transfer. The studies presented in this dissertation are an attempt to further understand charge transfer processes in semiconductor nanostructures, in particular, those occurring within the same nanocrystals. This is carried out by a combination of spectroscopic techniques and modelling. First, time-resolved fluorescence measurements are used to investigated surface trapping/de-trapping dynamics in CdSe and CdSe/CdS/ZnS core/shell/shell quantum dots. A kinetic model, in which trapping/de-trapping is described with Marcus' classical electron transfer theory, is used to analyzed our results, yielding excellent agreement between model and experiment. Second, the influence of temperature and solvent environment in the optical spectra of CdSe/CdTe nanorods are examined. Solvatochromic shifts in these heterostructures are found to be larger than those observed in core-only quantum dots. Finally, ultrafast dynamics and biexciton states in CdSe/CdTe quantum dots are probed using two-dimensional optical spectroscopy. The fine structure of the lowest exciton and biexciton states are calculated for a model system with type-II band-alignment and simulations of 2D spectra are performed.

In large molecular systems such as DNA, supramolecular complexes and dendrimers, functional groups located at different parts of the molecular structure can act as charge donors or acceptors, and photoinduced intramolecular charge transfer can occur. An analogous scenario can be found in colloidal semiconductor nanocrystals, most evident in type-II heterostructures, where the relative band-alignment of the constituent materials are in a stagger configuration. Such a configuration, provides an energetically favourable situation for an photo-generated electron to be transferred from one material to the other, confining the electron and the hole in different domains of the nanostructure. A less obvious scenario in nanocrystals is when the core is thought of as the donor group, and the surface as the acceptor group. In such a scenario, the localization of electron or hole at surface defect sites, a process that occurs in every nanocrystal, can be thought of as an ``intramolecular" charge transfer. The studies presented in this dissertation are an attempt to further understand charge transfer processes in semiconductor nanostructures, in particular, those occurring within the same nanocrystals. This is carried out by a combination of spectroscopic techniques and modelling. First, time-resolved fluorescence measurements are used to investigated surface trapping/de-trapping dynamics in CdSe and CdSe/CdS/ZnS core/shell/shell quantum dots. A kinetic model, in which trapping/de-trapping is described with Marcus' classical electron transfer theory, is used to analyzed our results, yielding excellent agreement between model and experiment. Second, the influence of temperature and solvent environment in the optical spectra of CdSe/CdTe nanorods are examined. Solvatochromic shifts in these heterostructures are found to be larger than those observed in core-only quantum dots. Finally, ultrafast dynamics and biexciton states in CdSe/CdTe quantum dots are probed using two-dimensional optical spectroscopy. The fine structure of the lowest exciton and biexciton states are calculated for a model system with type-II band-alignment and simulations of 2D spectra are performed.