Collisions between atoms in high Rydberg states and polar targets can lead to the formation of dipole-bound negative ions. We examine the dynamics of CH3CN- ion production through electron transfer in K(np)/CH3CN collisions using velocity selected Rydberg atoms. The CH3CN- ion formation rate decreases markedly with decreasing Rydberg atom velocity, principally as a consequence of postattachment electrostatic interactions between the product ions. Implemented using Monte Carlo techniques, a curve-crossing model, which considers the effect of crossings between the diabetic potential curves for the covalent K(np)/CH3CN system and the K+/CH3CN - system, provides a clear explanation of several characteristics seen in electron transfer in K(np)/CH3CN collisions including: the n dependence in the CH3CN- ion production rate, the velocity dependence in the CH3CN- ion production rate, and the relatively small rate constant ∼0.5 - 1.0 x 10-8cm3 s-1 for production of long-lived CH3CN - ions.

The vibrational spectra of $( eta sp5$-C$ sb5$H$ sb5$)Re(CO)$ sb3, ( eta sp5$-C$ sb5$Me$ sb5$)Re(CO)$ sb3, ( eta sp6$-C$ sb6$H$ sb6$)Cr(CO)$ sb2$(CS), Cr(CO)$ sb5$(CS), Re(CO)$ sb5$Cl, CH$ sb3$Re(CO)$ sb5$ and CH$ sb3$Mn(CO)$ sb5$ have been recorded under high pressures ($<$ 50kbar). Several phase transitions have been detected. The effects of pressure on the metal-ligand bonding interactions have been evaluated. The phase behaviour of C$ sb{60},$ K$ sb2$SnBr$ sb6$, K$ sb2$WO$ sb4$, K$ sb2$CrO$ sb4$ and Cs$ sb2$ (B$ sb{10}$Cl$ sb{10}$) has also been examined by high-pressure vibrational spectroscopy. / $ sp{13}$C chemical shift tensors and anisotropies have been obtained for $( eta sp6$-C$ sb6$H$ sb6$)Cr(CO)$ sb2$(CS), $( eta sp6$-C$ sb6$H$ sb6$)Cr(CO)$ sb3$, K (PtCl$ sb3( eta sp2$-C$ sb2$H$ sb4$)) and trans- (PtCl$ sb2( eta sp2$-C$ sb2$H$ sb4$)) $ sb2$. The CS ligand shielding ansiotropy is the largest ever observed for a $ sp{13}$C nucleus (530 ppm). $ sp{31}$P chemical shielding tensors have been determined for PPh$ sb3$, P(OPh)$ sb3, trans$-Cr(CO)$ sb4$(CS)(PPh$ sb3$) and trans-Cr(CO)$ sb3$(CS) (P(OPh)$ sb3$) $ sb2$. The results provide new insights into metal-phosphorus bonding interactions. / The molecular dynamics of the orientationally-disordered, cage hydrocarbons, 1-bromo- and 1-chloroadamantane, 1-adamantanecarboxylic acid and 2-adamantanone, have been investigated by $ sp{13}$C spin-lattice relaxation and dipolar dephasing time measurements. The motions in the disordered phases are different from those proposed on the basis of neutron scattering data. The phase behaviour of 1,3-dimethyladamantane has been studied by a combination of vibrational and proton NMR spectroscopy. The phase transitions in the cyclic hydrocarbons, cyclooctane, cyclooctanone and cyclohexanone, have been probed by vibrational spectroscopy. Unit cell symmetries have been proposed for all three compounds in their ordered phases. Cyclooctane and cyclooctanone form metastable phases. The different molecular motions in solid cyclohexanone have been established by $ sp2$H NMR lineshape analysis.

My thesis is organized as follows. First, I introduce a general overview on the nature of real proteins. Then I address the thermodynamics of proteins and how one can model it. After that I introduce a microscopic model for proteins and I discuss the reasons for its construction. After a thorough theoretical investigation of this model I make several predictions for its thermodynamic and dynamic behavior. I then introduce a dynamics for protein folding, including a master equation approach for the description of protein kinetics. Using the protein thermodynamics introduced earlier I implement some extensive Monte-Carlo computer calculation to elucidate the non Arrhenius modes in the protein folding. A mesoscopic model of the hierarchically constrained dynamics will be introduced after that to account for the observed behavior. Finally, I investigate an abstract but exactly solvable model which could serve as a cornerstone for the dream of protein designers---an ultimately fast folding protein. (Abstract shortened by UMI.)

<p> Single molecule magnets (SMMs), such as Mn₁₂-acetate, are composed of transition metal ions and consists of identical molecules with large ground-state spin (<i>S</i> = 10) and a strong uniaxial anisotropy (65 K). Below about 3 K, Mn₁₂-acetate exhibits magnetic hysteresis with steps at specific values of longitudinal magnetic field due to resonant quantum tunneling between spin up and down projections along the easy axis. The intermolecular exchange interactions between spins on molecules are quite small and spins are considered to be independent and non-interacting. </p><p> However, the molecules do interact with each other both through magnetic dipolar interactions and through the lattice (e.g. phonons). I have investigated collective effects in SMMs due to these intermolecular interactions. In the thesis I will present experiments that explored magnetic ordering due to magnetic dipole interactions in Mn₁₂-acetate and Mn₁₂-acetate-MeOH. I will also present exper- iments on the onset of magnetic de agration in Mn₁₂-acetate due to a thermal instability.</p><p> The magnetic ordering studies involved investigating the effect of transverse fields on the susceptibility of single crystals of Mn₁₂-acetate and Mn₁₂-acetate- MeOH. Transverse fields increase quantum spin uctuations that suppress long- range order. However, the suppression of the Curie temperature by transverse fields in Mn₁₂-acetate is far more rapid than predicted by the Transverse-Field Ising Ferromagnetic Model (TFIFM) and instead agrees with the predictions of the Random-Field Ising Ferromagnet Model. It appears that solvent disorder in Mn₁₂-acetate gives rise to a distribution of random-fields that further suppress long-range order. Subsequent studies on Mn₁₂-acetate-MeOH, with the same spin and similar lattice constants but without solvent disorder as Mn₁₂-acetate, agrees with the TFIFM.</p><p> The magnetic de agration studies involved studying the instability that leads to the ignition of magnetic deflagration in a thermally driven Mn₁₂-acetate crystal. When spins prepared in a metastable state reverse, Zeeman energy is released that diffuses away. In some circumstances, the heat released cannot be compensated by thermal diffusion, resulting in an instability that gives rise to a front of rapidly reversing spins traveling through the crystal. We observed a sharp crossover from relaxation driven by heat diffusion to a self-sustained reversal front that propagates at a constant subsonic speed.</p>

<p> Particles in turbulence flows, either natural or artificial, can be charged. According to the previous research, electrical charge on particles has an influence on both rain enhancement and particle clustering in turbulent flow. Due to the Lorenz effect of unipolar or bipolar charged particles, particles tend to attract or repel to each other. Moreover, it is well known that electrical field exists in the atmosphere that has an effect on charged particles, especially droplets. As a result, the dynamic behaviors of charged particles can be rather different from uncharged particles, which, to date, are not systematically studied yet.</p><p> In order to systematically investigate the charged particles, we developed a method involving holographic particle tracking velocimetry (HPTV) technique to study the kinetic behavior of charged particles in flow. Theoretical analysis was also carried out to correlate kinetic behavior of particles and charge amount on them. This thesis also validated the feasibility of this method. The results of the validation experiment show that this method is capable to measure the velocity and acceleration of particles. By means of the second-order polynomial regression of particles' motion, the average acceleration, initial position and initial velocity of particles were obtained. With the mathematical model of a product of two normally distributed variables, the error bounds in measurement of particle kinetics can be acquired. Therefore, combining with the electrical field and diameter range of particles, we can quantitatively study the dynamic behavior of charged particles in flow.</p><p> In order to verify this, some experiments were designed and performed. We applied this method to quantitatively measure the behavior of particles to acquire the charge amount on particles from an enclosed chamber used in turbulence experiments. The result showed that although the charge amount was very low, most particles were charged with positive charge in the enclosed chamber. This result agreed with the triboelectric effect theory that in the friction with PVC tube, glass bubble particles prefer to lose electron and show positive charge. We also studied the effect of fan speed and material on charge amount on particles. Our results show that, by means of changing the material of tube, particle charge level is reduced, although more theoretical and experimental research should be carried out to confirm this conclusion.</p>

<p> A Langmuir film, which is a molecularly thin insoluble film on a liquid substrate, is one practical realization of a quasi-two dimensional matter. The major advantages of this system for the study of phase separation and phase co-existence are (a) it allows accurate control of the components and molecular area of the film and (b) it can be studied by various methods that require very flat films. </p><p> Phase separation in molecularly thin films plays an important role in a range of systems from biomembranes to biosensors. For example, phase-separated lipid nano-domains in biomembranes are thought to play crucial roles in membrane function. I use Brewster Angel Microscopy (BAM) coupled with Fluorescence Microscopy (FM) and static Light Scattering Microscopy (LSM) to image phases and patterns within Langmuir films. The three microscopic techniques &mdash; BAM, FM and LSM &mdash; are complimentary to each other, providing distinct sets of information. They allow direct comparison with literature results in lipid systems. </p><p> I have quantitatively validated the use of detailed hydrodynamic simulations to determine line tension in monolayers. Line tension decreases as temperature rises. This decrease gives us information on the entropy associated with the line, and thus about line structure. I carefully consider the thermodynamics of line energy and entropy to make this connection. In the longer run, LSM will be exploited to give us further information about line structure. I have also extended the technique by testing it on domains within the curved surface of a bilayer vesicle. I also note that in the same way that the presence of surface-active agents, known as surfactants, affects surface energy, the addiction of line active agents alters the inter-phase line energy. Thus my results set to stage to systematically study the influence of line active agents &mdash;'linactants' &mdash; on the inter-phase line energy. </p><p> Hierarchal self-assembled chiral patterns were observed as a function of temperature. I found that the appearance of these domains could be explained with a simple uniaxial optical axis in the underlying structure, which is the first critical step to understanding the origin of these patterns.</p>

Lipid-cholesterol bilayers are studied by means of a microscopic multi-state lattice model and Monte Carlo computer simulations. The model used is a direct extension of the Pink model for the main transition of pure lipid bilayers. Cholesterol is introduced as a bulky, rigid molecule with no internal degrees of freedom. The model is able to account for the chain melting of lipid molecules, and is expected to be valid at low cholesterol concentrations. / A minimal model for the transport of ions across membranes is used to predict the changes in the passive permeability of lipid-cholesterol bilayers for different cholesterol concentrations and different lipid chain lengths. The model assigns different probabilities of transfer to bulk, clusters and interfaces. The main assumption is that, defects due to bad packing at interfacial regions, cause the membrane to be leaky and allow the ions to permeate it. Therefore the model assigns a high probability of transfer to the interfacial regions. / A peak in the permeability is observed near the transition temperature, which is in accord with experimental data. The results show an increase in the passive ion permeability for increasing cholesterol concentration for the three systems under consideration. Also, an increase in the membrane permeability is predicted for decreasing chain length for all the cholesterol concentrations studied.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 0832. Adviser: Taekjip Ha. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7404. Adviser: J. Gary Eden. Includes bibliographical references (leaves 87-91) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--Lehigh University, 2007.