<p>Studying the ultrafast dynamics of small molecules can serve as the first step in understanding the dynamics in larger chemically and biologically relevant molecules. To make direct comparisons with existing computational techniques, the photons used in pump-probe spectroscopy must make perturbative transitions between the electronic states of isolated small molecules. In this dissertation experimental investigations of ultrafast dynamics in electronic excitations of neutral ethylene and carbon dioxide are discussed. These experiments are performed using VUV/XUV femtosecond pulses as pump and probe. </p><p> To make photons with sufficient energy for single photon transitions, VUV and XUV light is generated by high harmonic generation (HHG) using a high pulse energy (&ap;30&ndash;40 mJ) Ti:sapphire femtosecond laser. Sufficient flux must be generated to enable splitting of the HHG light into pump and probe arms. The system produces >10¹⁰ photons per shot, corresponding to nearly 10 MW of peak power in the XUV. Using a high flux of high energy photons creates a unique set of challenges when designing a detector capable of performing pump-probe experiments. A velocity map imaging (VMI) detector has been designed to address these challenges, and has become a successful tool facilitating studies into molecular dynamics that were not possible before its implementation. </p><p> The emphasis on using high energy, single photon transitions allowed theoretical calculations to be directly compared to experimental yields for the first time. This comparison resolved a long standing issue in the excited state lifetime of ethylene, and provided a confirmation of the branching ratio between the two nonadiabatic relaxation pathways that return ethylene back to its ground state from the &pi;*. The participation of the 3s Rydberg state has also been measured by collecting the time resolved photoelectron spectrum during the dynamics on ethylene&rsquo;s &pi;* excited state, confirming calculations predicting the effect of the 3s. </p><p> In carbon dioxide the first time resolved measurement in the lowest electronic excitation of carbon dioxide has been performed. A high kinetic energy release channel shows the signature of wavepacket dynamics within the excited state manifold. Deviation from the direct dissociation predicted for the pumped state provides experimental evidence confirming theoretical predictions of nonadiabatic transitions within the lowest lying electronically excited states. </p>

Recent discoveries of low-loss, far-infrared transmitting halide glasses have sparked much interest in extending fiber-optic technology into the infrared region. However, a far greater than theoretical loss has been observed which has slowed research in the field. For this reason, computer modeling of several halide glass systems was performed in order to develop a fundamental understanding of the relationships between structural and optical properties of these glasses. ZrF₄, ZrF₄/BaF₂, ZnCl₂ glasses and melts were prepared using an isothermal-isobaric molecular dynamics algorithm. The infrared spectra were then calculated by Fourier transforming the dipole moment autocorrelation functions of the basic structural units. The more ionic ZrF₄ based glasses showed good agreement with experimental data, whereas the covalently bonded ZnCl₂ glass did not. Addition of barium to ZrF₄ glass was found to reduce high frequency modes of vibration in the glass.

A fundamental quantum-mechanical problem on the phase of quantum harmonic oscillators, which has remained an enigma for more than sixty years since the first treatment by Dirac, is completely solved. Contrary to the common belief that no Hermitian phase operators can be found to describe the phase properties of a quantum harmonic oscillator, a well-defined Hermitian phase operator with an appropriate classical limit is constructed unambiguously. The approach is different in nature from those of many previous attempts which were more or less based on the idea of polar decomposition of the annihilation operator. The fundamental difference between the quantum phase and the classical phase in spite of their conceptual consistency is pointed out and explained. The eigenvalue spectrum and eigenstates of the phase operator are obtained. Some important properties of the phase operator and phase states are investigated. / The rest of this research is devoted to the studies of multimode Gaussian squeezed states of quantum harmonic oscillators. Multimode squeeze operators and rotation operators are defined such that they have extremely similar algebraic properties as those of their single-mode counterparts. It is shown that the introduction of N-mode squeeze operators provides a convenient set of parameters to describe squeezing in multimode Gaussian squeezed states. The disentangling, normal ordering, and some other properties of N-mode squeeze operators are investigated. It is also shown that the time-evolution operator for a general N-mode quadratic Hamiltonian can be conveniently expressed as an operator product containing an N-mode squeeze operator, an N-mode rotation operator, and an N-mode displacement operator. As an application of this result, the dynamics of N-mode harmonic oscillators with time-dependent normal coordinates and frequencies is investigated and formulated by the use of these N-mode unitary operators. A general expression for the time-dependent transition amplitudes between two arbitrary N-mode boson number states is obtained and explicit results are given for the case of sudden changes in normal coordinates and frequencies. / Source: Dissertation Abstracts International, Volume: 50-12, Section: B, page: 5703. / Major Professor: William Clifford Rhodes. / Thesis (Ph.D.)--The Florida State University, 1989.

This dissertation addresses the dynamic interactions in ion-molecule collisions. Theoretical methods are developed for single and multiple electron transitions in fast collisions with diatomic molecules by heavy-ion projectiles. Various theories and models are developed to treat the three basic inelastic processes (excitation, ionization and charge transfer) involving one and more electrons. The development, incorporating the understanding of ion-atom collision theories with some unique characteristics for molecular targets, provides new insights into phenomena that are absent from collisions with atomic targets. The influence from the multiple scattering centers on collision dynamics is assessed. For diatomic molecules, effects due to a fixed molecular orientation or alignment are calculated and compared with available experimental observations. Compared with excitation and ionization, electron capture, which probes deeper into the target, presents significant two-center interference and strong orientation dependence. Attention has been given in this dissertation to exploring mechanisms for two- and multiple electron transitions. Application of independent electron approximation to transfer excitation from molecular hydrogen is studied. Electron-electron interaction originated from projectile and target nuclear centers is studied in conjunction with the molecular nature of target. Limitations of the present theories and models as well as possible new areas for future theoretical and experimental applications are also discussed. This is the first attempt to describe multi-electron processes in molecular dynamics involving fast highly charged ions / acase@tulane.edu

Polyelectrolyte conformation, interactions and hydrodynamics show a marked dependence on the ionic strength (C$\sb{\rm s}$) of the medium, the concentration (C$\sb{\rm p}$) of the polymer itself and their charge density ($\xi$). The apparent electrostatic persistence length obtained from static light scattering varied approximately as the inverse square root of C$\sb{\rm s}$ for highly pure, high molecular weight hyaluronate (HA) as well as for variably ionized acrylamide/sodium acrylate copolymers (NaPAA), and linearly with $\xi$. The experimental values of persistence length and second virial coefficient (A$\sb2$) are compared to predictions from theories based on the Debye-Huckel approximation for the Poisson-Boltzmann equation and on excluded-volume. Although the mean square radius of gyration ($\rm\langle S\sp2\rangle$) depended strongly on C$\sb{\rm s}$. $\rm\langle S\sp2\rangle$ decreasing with increasing C$\sb{\rm s}$ for both HA and NaPAA indicating clear evidence of polyion expansion, dynamic light scattering values of the translational diffusion coefficient (D) remains constant when extrapolated to infinite polymer concentration for both the polymers. The behavior of D is compared to predictions from coupled mode theory in the linear limit. The effects of NaOH on the conformations, interactions, diffusion and hydrolysis rates of HA are characterized in detail using static, dynamic and time-dependent light scattering supplemented by size exclusion chromatography (SEC). For the HA $\rm\langle S\sp2\rangle,\ A\sb2$ and the hydrolysis rates all resemble superposing titration curves, while the D remains independent of both the concentration of NaOH, and the contraction of $\rm\langle S\sp2\rangle$. The indication is that the interactions, conformations and the hydrolysis rates are all controlled by the titration of the HA hydroxyl groups by the NaOH to yield -O$\sp-$, which (i) destroys single strand hydrogen bonds, leading to de-stiffening and contraction of the HA coil and a large decrease in intermolecular interaction, and (ii) slowly depolymerizes HA. The experimental results of HA depolymerization is compared to predictions from the theory of random scission. PGM depolymerization is carried out with (i) NaOH, (ii) hyaluronidase, (iii) HCl. These agents degraded the polymer in different ways. NaOH apparently stripped off the GAG chains from the protein backbone. Hyaluronidase seemed to randomly cleave the GAG sidechains, while HCl both stripped the GAG sidechains and randomly cleaved the protein backbone. Time dependent static light scattering of each degradation mechanism traced out its own characteristic signature of reciprocal scattered intensity versus time, models for which are presented. This technique allows degradation mechanisms, associated rates and percentage of material in the backbone and sidechains to be determined. The presence and removability of the 'extraordinary' diffusional phase (EP) at low ionic strength are investigated exhaustively for HA, NaPAA, polystyrene sulfonate, poly(L)lysine, heparin and chondroitin sulfate. The EP is found to be always removable by filtration through a sufficiently small pore-size membrane / acase@tulane.edu

Rhodopsin is a seven transmembrane helix GPCR found which mediates dim light vision, in which the binding pocket is occupied by the ligand 11- cis-retinal. A site-directed ²H-labeling approach utilizing solid-state ²H NMR spectroscopy was used to investigate the structure and dynamics of retinal within its binding pocket in the dark state of rhodopsin, and as well the MetaI and MetaII. 11-cis-[5-C²H₃]-, 11-cis-[9-C²H₃]-, and 11-cis-[13-C²H₃]-retinal were used to regenerate bleached rhodopsin. Recombinant membranes comprising purified rhodopsin and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) were prepared (1:50 molar ratio). Solid-state ²H NMR spectra were obtained for the aligned rhodopsin/POPC recombinant membranes at temperatures below the order-disorder phase transition temperature of POPC. The solid-state NMR studies of aligned samples, give the orientations of the ²H nuclear coupling tensor relative to the membrane frame, which involve both the conformation and orientation of the bound retinal chromophore. Theoretical simulations of the experimental ²H NMR spectra employed a new lineshape treatment for a semi-random distribution due to static uniaxial disorder. The analysis gives the orientation of the ²H-labeled C-C²H₃ methyl bond axes relative to the membrane plane as well as the extent of three-dimensional alignment disorder (mosaic spread). These results clearly demonstrate the applicability of site-directed ²H NMR methods for investigating conformational changes and dynamics of ligands bound to rhodopsin and other GPCRs in relation to their characteristic mechanisms of action.

The technique of pulsed-beam Fourier transform microwave spectroscopy is applied to gas-phase organometallic systems for elucidation of fundamental structural properties of the compounds. Ten organometallic species with significant catalytic and reactive properties are examined and presented. This work includes complete three-dimensional structural determinations of; methylrheniumtrioxide, cyclopentadienylthallium, tetracarbonyldihydroiron, tetracarbonyldihydroruthenium and tetracarbonylethyleneiron. Quadrupole coupling parameters are presented and discussed for the compounds; methylrheniumtrioxide, cyclopentadienylrheniumtricarbonyl, cyclopentadienylindium, 'anti' and ' syn' allyltricarbonylironbromide, chloroferrocene and bromoferrocene. Partial structural determinations are given for cyclopentadienylindium, ' anti' allyltricarbonylironbromide, chloroferrocene and bromoferrocene.

The recent discovery of photorefractive polymer composites with near 100% four-wave-mixing diffraction efficiency and high net optical gain by the author and coworkers at the University of Arizona has forwarded the advances of using organic materials to fabricate nonlinear optical devices. Nonlinear optical chromophores provide the optical properties for these new materials. Since there are thousands of molecules that are potential candidates to yield high performance nonlinear optical materials, a technique to quickly characterize the optical properties of these molecules is clearly needed. We have developed a frequency-dependent ellipsometric technique that simultaneously determines the first-order (anisotropic polarizability), second-order (first-hyperpolarizability), and third-order (second-hyperpolarizability) optical molecular coefficients of the chromophore. In this dissertation we will discuss the physics of these high performance nonlinear optical organic materials, and the characterization of their unique properties, leading to the development of our frequency-dependent ellipsometric technique. The technique itself will be discussed in detail, with an analysis of the molecules that are best suited for this type of measurement scheme, and a discussion of the limitations of this technique. Experimental data will be presented for a typical high performance nonlinear optical chromophore 4-(4'-nitrophenylazo)-1,3-di((3''- or 4''-vinyl)benzyloxy)benzene (NPADVBB).

Prehydrolyzed n-octadecyltriethoxysilane (OTE) molecules were self-assembled as a monolayer on both untreated and argon/water vapor plasma-treated mica. The properties and stability of these monolayers have been qualitatively and quantitatively investigated with a surface forces apparatus (SFA) under various environmental conditions The interaction force between the OTE monolayers immersed in water showed that plasma treatment reduced the range of the steep short-range repulsion and motivated the water vapor studies. The humidity tests revealed a substantial monolayer swelling in the untreated case at 95% RH or higher but there was no swelling in the plasma treated case. Furthermore, adhesive force measurements as a function of variations in environmental conditions such as temperature, relative humidity, contact time, and high stress showed that the plasma treated OTE monolayer appears to be more stable than the untreated monolayer in high humidities. In dry conditions both rnonolayers are molecularly smooth, well ordered and highly compact as well as mechanically robust and tenacious. Finally, the thickness compressibility studies in both dry and humid conditions suggested that the OTE phase state for both the plasma treated and untreated cases is pseudo-crystalline. Further, these studies suggested that the monolayer on both plasma treated and untreated mica does not fully cover the entire surface and likely exists as two very discrete phase states composed of large crystalline polymerized OTE domains and somewhat hydrophilic gaseous regions. The results from several different SFA experiments strongly indicates the OTE-SAM is covalently attached at least partially to the plasma treated mica while the monolayer weakly physisorbs to the untreated mica surface. Accordingly, due to the covalent connection, the OTE-SAM on plasma treated mica is more stable particularly in highly humid or even completely wet environments although it is thought the monolayer does not fully cover the mica surface.

Ionization of xenon atoms excited to the lowest states in the n=17 and n=20 Stark manifolds at atomically flat Au(111) surfaces and at heavily-doped n-type and p-type Si(100) surfaces having robust native oxide layers is examined over a range of incident angles. Ionization is characterized by resonant surface ionization with contributions from local fields at the surface associated with surface charging or surface inhomogeneities. For oxidized semiconducting surfaces the local fields are a factor of two to three times larger than for conducting surfaces leading to markedly different results.