No description available.

Interactions between Mn12–acetate molecular magnets and thin gold films have been explored in light of the theory of weak localization. Low-temperature measurements of the magnetoresistance of gold films of varying thicknesses, with and without the presence of a surface layer of Mn12–acetate, have been performed using a dilution refrigerator. Quantitative fits to the data using the predictions of weak localization theory were performed using a least-squares fit method in order to determine characteristic times for elastic, inelastic, spin-orbit and spin scattering events within the gold. These data indicate that the presence of Mn12–acetate on the surface of the gold film leads to a significant enhancement of the spin scattering within the gold films.

We used self-assembling tunnel junctions (SATJs) to study the electron transport through films of the molecular magnets, Mn12-Acetate. Pulse laser deposition (PLD) was used to deposit two monolayers of Mn12-Acetate on thin Pt wires (diameter 0.001 in). The electron tunneling current was measured with typical bias voltages from -1 to 1 V at liquid helium temperature, 4.2 K. I, dI/dV , and d2I/dV 2 signals were directly acquired with the aid of a current amplifier and two lock-in-amplifiers. Results show that the differential conductance is approximately 10â 6 S for bias voltages 0.04 V < or =| V |< or = V and exhibits a strong voltage dependence. In the region | V |< or = 0.04 V, we find a zero-bias feature (ZBF) in which the differential conductance is suppressed. In some samples, we observe I -V staircases which we attribute to electrons "hopping" between the electrodes and the molecules. The observed hysteresis was attributed to the slow relaxation of molecules re-orienting within the junction. Abrupt conductance jumps at a bias voltage of -0.12 V were also observed and may indicate state transitions in the Mn12-Acetate molecules. Furthermore, we observed that the zero bias feature (ZBF) can switch from an enhancement to a suppression of the differential conductance. A dip and dry (DAD) method was also used to form films of Mn12-Acetate on Al and Pt wires. Although the conductances were similar to those obtained using the PLD method, there were some subtle differences. In particular, we did not observe the I -V staircases and the state jumps were more ambiguous. The differential conductance for the Mn12-Acetate films on Al wires were typically 10- 7 S, which we attributed to the oxide layer on Al surfaces. We have also found substantial changes in the I - V characteristics when the Pt wires coated with the Mn12-Acetate films were stored in 10-2 Torr for 6 months. In particular, we observed many new features such as peaks in the conductance as a function as the bias voltage. We believe that these effects may be caused by the slow oxidation of the Mn12-Acetate molecules.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1953. / Includes bibliographical references (leaves 73-75).

Not available / text

No description available.

This thesis is concerned with attempts to establish solid-state NMR as a complementary technique to X-ray crystallography for providing information on crystal structure, i.e. information regarding conformation, packing and inter- or intra-molecular interactions. Methods of assigning the solid-state NMR spectrum have been used which rely upon (^1)H-(^13)C dipolar interactions and upon the shielding anisotropy experienced by the nuclei. Single pulse experiments have also been used to identify solvate molecules. Of particular importance, the anisotropy and asymmetry have been found for a number of steroids, and the values used to assign the high frequency region of the spectrum. This has enabled chemical shifts to be linked to the hydrogen bonds that are present. Thus, the mode of hydrogen bonding can be predicted in forms of cortisone acetate for which the crystal structure is not available. Chemical shifts have also been linked with the conformation of the D ring. In this way, important crystallographic information has been gleaned from the solid-state NMR spectrum. The effect of the formation of hydrogen bonds upon the shielding tensor components of carbonyl and ester carbons has been studied, and found to cause a high frequency shift in δ22, which is probably oriented along the C=0 bonds. This leads to a high frequency shift in the isotropic chemical shift. The effect of the spinning speed upon the centreband intensity of a peak as the anisotropy and asymmetry are varied has been investigated. It has been found that at low spiiming speeds, the centreband intensity does not vary in a simple fashion. Thus it is recommended that full shielding tensor analysis is performed. The effect of the spinning speed on the sample temperature has also been studied. Results show that at low spinning speeds (up to 2 kHz) there is sample cooling as the spinning speed increases (attributed to the Joule -Thompson effect). But at higher spinning speeds (above 2 kHz) then there is sample heating as the spinning speed increases. The importance of this result is discussed. The effect of quadrupolar nuclei (35C1 and (^14)N) upon the spectrum of a spin-(^1)(_2) nucleus ((^13)C) has been studied. In favourable cases, the anisotropy in the spin-spin coupling constant has been found, whilst in other cases, the sign and magnitude of the quadrupolar coupling constant have been obtained. The broadening of resonances of carbon atoms adjacent to quadrupolar nuclei has been valuable in assigning the solid-state NMR spectra. The broadening effect has also been observed at more distant sites. It has not been possible to distinguish the effects of (^37)C1 and (^35)C1 on the carbon spectra of chlorine containing steroids.

The oxidation of 4-t-butyltoluene in glacial acetic acid by hydrogen peroxid in a process catalysed by cobalt(II) acetate tetrahydrate and sodium bromide has been studied with the aim of increasing the selectivity towards 4-t-butylbenzaldehyde.

Thesis (M.S.)--University of Wisconsin--Madison, 1983. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 228-230).