Dissociative and non-dissociative electron attachment processes are investigated via electron transfer in collisions between velocity selected Rydberg atoms and target molecules. Measurements of the velocity distribution of the reaction products and of the decay of product negative ions during passage to the detector provide information about the energetics of the interactions and about the lifetime of the intermediate negative ion formed. Collisions with CBrCl 3 result in a dissociative process producing Br- and Cl- as products. Br- production occurs through two reaction channels. The intermediate negative ion dissociates immediately in one channel, but the second channel involves a long-lived intermediate having a lifetime of ∼5 ps. A single reaction channel produces Cl -, but it is uncertain if the process is immediate or if it occurs after a few vibrational periods of the intermediate ion. Non-dissociative electron attachment occurs with C7F14 and with C 6F6. Collisions with C7F14 lead to the production of free electrons and of long-lived (tau > 100 mus) C 7F14-- ions. The free electrons, which result from autodetachment, are all created within a very short time period (tau ≲ 15 ps) following initial electron capture. Collisions with C6F6 result in the formation of C6F 6-* ions that have a broad range of lifetimes against autodetachment. Data analysis and model calculations are discussed in addition to possible theoretical models explaining the results. Future experimental studies are also proposed.

Dissociative and non-dissociative electron attachment processes are investigated via electron transfer in collisions between velocity selected Rydberg atoms and molecules. Low-energy dissociative electron attachment to BrCN and CBrCl 3, over the temperature range 300 to 450K, is examined, by measuring the velocity and angular distributions of negative ions produced. Measurements for BrCN indicate that electron capture leads to the formation of transient BrCN-* ions that dissociate with a mean lifetime tau ∼20 ps to form CN- product ions. No significant Br - production was observed over the present temperature range. Electron transfer to CBrCl3 leads to the formation of both Cl - and Br- ions. The branching ratio of the reaction pathways dramatically changes with temperature. Investigation of non-dissociative electron attachment to C6H6 indicates that benzene anions are formed with lifetimes of ∼3 ps. Influence of a strong applied electric field on background processes like blackbody photoionization and collisional photo ionization, which complicate studies of Rydberg atom collision processes, is analyzed and the results presented.

A study is presented of the photophysics of a variety of fullerene derivatives, including C60O, C70O, C120, 1,2-C70 H2, Kr C60, and four mono-substituted benzo-adducts of C70. Measured photophysical properties include UV-vis absorption, triplet triplet absorption, temperature dependent triplet decay kinetics, fluorescence and phosphorescence emission, and triplet quantum yields. The findings for these compounds are tabulated and compared to those of similar derivatives. Trends in the properties are identified where possible. Temperature dependent studies of C60O reveal two distinct regimes of triplet decay, with very different activation energies. Reversible opening of the C-C epoxide bond is suggested as the source of this unusual behavior. C60O is also found to efficiently quench C60 triplets, with a bimolecular quenching constant of 3.6 +/- 0.6 x 109 M--1 s--1. Preliminary data on C70O suggest that its kinetic behavior resembles that of C60O, while spectrally it resembles other C70 derivatives. C120, the dimer of C60, dissociates into C 60 upon application of sufficient heat or light. Isosbestic points are found in the UV-vis spectra of C120/C60 mixtures, allowing absorptivity calibration of the C120 spectrum. The photolysis of C120 is found to proceed via the triplet state, with an activation energy of 5,500 cm--1 and a dissociative quantum yield of 2 x 10--3 at 297 K. A method based on energy transfer kinetics is used to determine the T1 energy of C 120. Kr C60, an endohedral van der Waals complex, is studied using UV-vis absorption spectroscopy and triplet-triplet kinetic spectroscopy. The results show small but distinct couplings of the C60 pi-electrons with the krypton atom. The photophysics of 1,2-C70H2 is thoroughly explored and compared to C70 and other fullerene derivatives. At higher temperatures, thermally activated S1 → S0 internal conversion becomes a major unexpected channel for triplet decay. Finally, the effect of derivatization site is explored using four benzo-adducts of C70. Some photophysical properties, such as triplet lifetime and wavelength of maximum triplet absorption, vary greatly, and may correlate with addend distance from the molecule's pole. Other properties, such as singlet and triplet energies, seem not to show such a correlation.

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.

The outer membranes of Gram-negative bacteria are highly asymmetric, with the inner leaflet composed of phospholipids and the outer leaflet mostly of lipopolysaccharides (LPS). The outer membrane is thought to act as a protective and permeability barrier, but is somehow permeable to various antimicrobial peptides. To study this problem we prepared oriented multilamellae of bilayers composed of pure LPS. X-ray diffraction showed that the samples produced good spectrum. The liquid crystalline to gel transition was observed by the appearance of a sharp peak corresponding to 4.23A and coexistence of two lamellar diffraction series. Phase diagrams of mutant LPS's were constructed as functions of temperature and the level of hydration. Electron density profiles were constructed, and compared with the program calculated model electron profiles, the peak position in the electron density profile was determined as the position of the phosphate atom in LPS molecule. Inorganic ions like Sodium(Na +), Potassium(K+), and Barium(Ba++) were added into the sample. Results showed that with the presence of the ions, the phase transition temperature of LPS mutant decreased, and the ions bound to the site where the phosphate atom located. Also, beta-sheet peptide protegrin-1 was added in the LPS sample. Results implied the peptide inserted in the headgroup of the LPS bilayer.

Broadly defined as fluids possessing multiple length scales, complex fluids, typified by polymers, hydrocarbons, surfactants, emulsions etc., exhibit microstructures even when macroscopically homogeneous. This dissertation introduces a classical density functional theory (DFT) that provides structural and thermodynamic information at the molecular level in these fluids near interfaces and in confinement. The microstructure in such systems is a function of both fluid and substrate characteristics, and varies on the order of molecular length scale (sometimes even smaller). The developments presented here can be broken down into two components that separately focus on the fluid and the interface aspects of the system. On the fluid side, the theory provides a very simple method for modeling polymeric mixtures, by treating the polyatomic system as a strongly associating atomic fluid mixture. Derived in terms of segment density, it offers accuracy comparable to the computationally intensive multi-point-density-based theories at a modest expense comparable to those of atomic DFTs. Comparisons with molecular simulations demonstrate its capability to accurately capture the entropic and enthalpic effects dictating the microstructure in inhomogeneous solutions and blends of linear and branched chains. On the interface side, the DFT provides the capability to describe adsorption of associating fluids on functionalized surfaces. These surfaces are activated with polar sites to which fluid molecules can bond, such as water adsorbing on activated carbon, silica, clay minerals, etc. The theory, in excellent agreement with simulations, shows that surface association significantly changes the fluid structure and adsorption behavior. An impressive feature of the theory enables one to estimate the distribution of fluid along the interface, i.e., the three-dimensional (3D) structure, while retaining the one-dimensional (1D) form. This translates into orders of magnitude of savings in computation time. The DFT is based on thermodynamic perturbation theory of the first order (TPT1), which is also the basis of the most widely used theory for bulk polymer solutions and melts---Statistical Associating Fluid Theory (SAFT). This consistency facilitates a seamless integration of the two into a common platform to model combined bulk-interfacial phase behavior and microstructure. This is of critical importance to several applications where interfacial properties need to be predicted based on bulk conditions.

Absolute differential and integral charge transfer cross sections have been measured for 0.5, 0.85, 1.5, 2.8, and 5.0 keV O$\sp+$ with O$\sb2$ at scattering angles between 0.01$\sp\circ$ and 3.50$\sp\circ$ in the laboratory frame. The dependence of these cross sections upon the electronic state of the O$\sp+$ ion was investigated. This study was performed using a filter cell technique to derive the cross sections for both the $\rm O\sp+(\sp4S)$ ground state ions and the $\rm O\sp+({\sp2D,\ \sp2P})$ metastable state ions. The charge transfer cross sections involving the $\rm O\sp+({\sp2D,\ \sp2P})$ ions are significantly larger than the corresponding cross sections for the ground state ions. Previously published cross section measurements are compared to the present results for the total integral charge transfer cross sections of state-selected keV O$\sp+$ with O$\sb2$.

Collisional energy removal rates from vibrationally excited T$\sb1$ pyrazine are measured using the refined and validated Competitive Radiationless Decay (CRD) method. Optical excitation followed by intersystem crossing prepares a vibrationally excited vapor sample of T$\sb1$ pyrazine. $\rm T\sb{n}\gets T\sb1$ transient absorption kinetics, measured with a S/N ratio of ca. 1000, provides the collisional dependence of the average triplet radiationless decay rate constant. Using a calibration between this decay constant and the triplet vibrational energy, the collisional history of the sample's vibrational energy content is deduced. This leads to the rate of collisional energy removal as a function of the triplet pyrazine's vibrational energy content. Results with a variety of small relaxers comprise the most useful database to date on collisional vibrational relaxation of a triplet state polyatomic. We find the following order of relaxer effectiveness per collision:$$\rm He{<}H\sb2{<}Ne{<}D\sb2{<}Ar{<}N\sb2{<}Kr{<}Xe{<}CO{<}CH\sb4{<}CO\sb2{<}H\sb2O$$These triplet state energy removal rates exceed those recently reported for vibrationally excited ground state pyrazine by a factor of ca. 7. In addition, a new method for determining the distribution of vibrational energy contents in an excited polyatomic sample is applied to vibrationally excited T$\sb1$ pyrazine. The T$\sb1$ population decays with a distribution of rate constants corresponding to the underlying distribution of vibrational energies. This rate constant distribution is extracted from decay kinetics through the use of a multi-Gaussian distribution model. The calibration between decay constant and triplet vibrational energy is used to deduce the molecular vibrational energy distribution, providing the first experimental view of an excited sample's vibrational energy distribution. Relatively narrow nascent vibrational energy distributions are progressively broadened during the early collisional encounters with a relaxer. These new vibrational energy distributions and the collisional energy removal results suggests a threshold for enhanced relaxation near 2000 cm$\sp{-1}$ of donor vibrational energy. These intriguing results should stimulate further theoretical and experimental research into the collisional relaxation of electronically excited molecules.

Low-energy electron transfer between a Rydberg atom and a target molecule can result in formation of long-lived metastable negative ions. Here we describe a novel permanent-magnet Penning trap designed to examine the lifetime of such long lived metastable negative ions. With the help of ion trajectory calculations, the characteristics of the trap have been investigated and the most effective methods for ion injection have been established. Collisions with SF6, which has a high electron attachment rate, result in the formation of SF-*6 ions which are known to have a long intermediate lifetime. Comparisons between experimental SF-*6 trapping data and ion trajectory calculations are discussed that demonstrate the capabilities of the trap. Future experimental studies are also proposed.

This work describes intensity saturation of photoassociative transitions of 86Sr at the quantum mechanical unitarity limit. The saturation behavior, which results in a roll-over of the photoassociation rate for intensities greater than the saturation intensity, features interesting physics. Unlike other photoassociation spectroscopy (PAS) experiments, photoassociation occurs in a magneto-optical trap operating on the narrow dipole-forbidden transition at 689 nm. A laser red-detuned from the principal atomic transition at 461 nm by as much as 1300 GHz induces the photoassociation of ground state atoms to excited molecular states. Our previous studies [1] suggest that some of the PAS transitions for 86Sr are sensitive to the intensity of the laser. This work delves more deeply into these high intensity PAS effects, a subject that has not, to our knowledge, been studied experimentally for alkaline-earth atoms.