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DAMAGE TO MITOCHONDRIAL ELECTRON TRANSPORT AND ENERGY COUPLING BY VISIBLE LIGHT

Description: Plutonium is one of the principal materials of both commercial and military nuclear power. It is produced primarily in fission reactors that contain uranium fuel, and its importance arises from the fact that a large portion of the plutonium produced is fissile: like uranium 235, the mass 239 and 241 isotopes of plutonium can be caused to fission by neutrons, including those with low energy. Because such fission events also release neutrons, substantial amounts of energy can be extracted from plutonium in a controlled or an explosive nuclear chain reaction. Now that commercial nuclear reactors provide a noticeable fraction of United States (and world) electrical energy, these reactors account for most plutonium production. For the most part, this material now remains in the irradiated fuel after removal from reactors, but should this fuel be reprocessed, the plutonium could be recycled to provide part and even most of the fissile content of fresh fuel. For the current generation of water-cooled reactors, the amount of plutonium to be recycled is substantial. In fast breeder reactors, designed to produce more fissile material than they destroy, considerably larger quantities of plutonium would be recycled. In other types of advanced reactors, particularly those which depend heavily on thorium as the material from which fissile material (primarily uranium 233) is produced, the amount of plutonium to be handled would be considerably reduced. Because plutonium is a highly toxic substance, great care is taken to contain it at the sites and facilities where it is stored or handled. In addition, it is necessary that devices be available to monitor any releases from these facilities into environmental media and to measure concentrations of plutonium in these media. The radiation protection standards are so strict for plutonium that only small releases and low concentrations can be tolerated. Such considerations, ...
Date: September 1, 1977
Creator: Aggarwal, B.B.; Quintanilha, A.T.; Cammack, R. & Packer, L.
Partner: UNT Libraries Government Documents Department

SENSITIVE OPTOACOUSTIC DETECTION OF CARBON MONOXIDE BY RESONANCE ABSORPTION

Description: Sensitive (0.15 ppm) and unambiguous detection of carbon monoxide is reported and a comparison of acoustically resonant and nonresonant detectors is given. The pressure dependence of the optoacoustic signal is discussed in the context of atmospheric absorption.
Date: October 1, 1977
Creator: Gerlach, R. & Amer, N.M.
Partner: UNT Libraries Government Documents Department

THE ROLE OF BUFFER GASES IN OPTOAOOUSTIC SPECTROSCOPY

Description: The dependence of an acoustically resonant optoacoustic signal on the molecular weight, and thermodynamic and transport properties of the buffer gas is reported. Our results show that careful selection of such gases can significantly increase the sensitivity and flexibility of optoacoustic spectroscopy. We also demonstrate that such thermodynamic quantities as {gamma} ({triple_bond} C{sub p}/C{sub v}) and sound velocity can now be measured readily and accurately. Other potential applications are suggested.
Date: November 1, 1977
Creator: Thomas III, L.J.; Kelly, M.J. & Amer, N.M.
Partner: UNT Libraries Government Documents Department

ELECTRON MICROSCOPY OF SOME RARE EARTH-COBALT ALLOY MAGNETS

Description: Transmission electron microscopy is being used to characterize the microstructural features in some 1:5 and 2:17 RE-Co magnets. In 2:17 compounds containing Fe and Mn, lamellae of hexagonal and other po1ytypic regions embedded in the rhombohedral matrix are observed. It is shown that the interface between the hexagonal and rhombohedral phases can be described as a stacking fault with fault vector normal to the interfacial plane. APB's parallel to the prism planes in the rhombohedral structure have also been identified and characterized. In contrast, no planar faults have been observed in the 1:5 materials containing misch metal as the major rare-earth component. In these alloys extensive twinning and precipitation of a 2:17 rhombohedral phase are the major microstructural features observed. The influence of these microstructures on the magnetic properties are discussed.
Date: October 1, 1977
Creator: Mishra, R. K. & Thomas, G.
Partner: UNT Libraries Government Documents Department

EROSION PREDICTION NEAR A STAGNATION POINT RESULTING FROM ENVIRONMENTAL SOLID PARTICLES

Description: Predicting the erosion that results from a gas-solid particle flow in coal energy conversion systems is crucial for the successful operation of coal gasification, magnetohydrodynamic power, and coal-fired turbine facilities. In this study the coupled gas-particle momentum equations are analytically solved to determine the particle trajectories near a plane stagnation point. The momentum equilibration parameter, which is a physical parameter measuring a particle's momentum, is found to be the unique criterion for predicting particle trajectories. It is shown that values of this parameter less than one-fourth identify particles that never impact with a wall. The closed-form solution obtained is used to predict the quantity of material removed from a wall as well as the location of erosion along the wall. The maximum erosion is calculated to occur for the momentum equilibration parameter taking a value of 2.3. The erosion rate is found to be proportional to the particle velocity raised to the exponent of 3.8.
Date: November 1, 1977
Creator: Laitone, J.
Partner: UNT Libraries Government Documents Department

EVIDENCE FOR THE ITINERANT ELECTRON MODEL OF FERROMAGNETISM AND FOR SURFACE PHOTOEMISSION FROM ANGLE-RESOLVED PHOTOEMISSION STUDIES OF IRON

Description: Angle-resolved HeI photoemission spectra of Fe(001) are reported and interpreted within the framework of a direct transition model using Callaway's ferromagnetic band structure. The generally good agreement between predicted and experimental peak positions is taken to be strong support for the itinerant electron theory of ferromagnetism. Spectra taken with nearly grazing incidence p-polarized light emphasize the one-dimensional density of states peaks, supporting Kliewer's theoretical predictions of surface photoemission. The importance of electron refraction is noted, as is the value of interpolation calculations for interpreting ARP spectra.
Date: October 1, 1977
Creator: Kevan, S.D.; Wehner, P.S. & Shirley, D.A.
Partner: UNT Libraries Government Documents Department

FINITE ELEMENT METHOD FOR SUBSURFACE HYDROLOGY USING A MIXED EXPLICIT-IMPLICIT SCHEME

Description: The mixed explicit-implicit Galerkin finite element method developed previously by the authors is shown to be ideally suited for a wide class of problems arising in subsurface hydrology. These problems include confined saturated flow, unconfined flaw under free surface conditions subject to the Dupuit assumption, flow in aquifers which are partly confined and partly unconfined, axisymmetric flow to a well with storage, and flow in saturated-unsaturated soils. A single computer program, entitled FLUMP, can now handle all of these problems. The mixed explicit-implicit solution strategy employed in the program insures a high level of accuracy and computation efficiency in most cases. It eliminates many of the difficulties that groundwater hydrologists have been encountering in trying to simulate extensive aquifer systems by finite elements. Some of the outstanding features of this solution strategy include an automatic control of time step size, reclassification of nodes from explicit to implicit during execution, automatic adjustment of the implicit time weighting factor, and the treatment of boundary conditions and source terms as arbitrary functions of time of the state of the system. Five examples are presented to demonstrate the versatility and power of this new approach. A purely physical derivation of the finite element equations which does not rely on the Galerkin formalism is also included in one of the appendices.
Date: August 1, 1977
Creator: Narasimhan, T.N.; Neuman, S.P. & Witherspoon, P.A.
Partner: UNT Libraries Government Documents Department

INITIAL RESULTS WITH THE BERKELEY ON-LINE MASS SEPARATOR - RAMA

Description: We have for some time been interested in developing a reasonably fast and universal (having little or no chemical selectivity) on-line mass analysis system to expand our capabilities in studying nuclei far from stability. The system selected was originally proposed by Nitschke and is termed RAMA an acronym for Recoil Atom Mass Analyzer. Basically, this system utilizes the helium-jet method to transport activity to a Sidenius hollow-cathode ion source which is coupled to a mass spectrometer. A comprehensive discussion of RAMA will appear elsewhere.
Date: November 1, 1977
Creator: Cerny, J.; Moltz, D.M.; Evans, H.C.; Vieira, D.J.; Parry, R.F.; Wouters, J.M. et al.
Partner: UNT Libraries Government Documents Department

THE EFFECT OF MAGNETICALLY ALIGNED POWDER ON THE MAGNETOSTRICTION OF SINTERED RARE EARTH - IRON LAVES PHASE COMPOUNDS

Description: A powder metallurgical approach is utilized to prepare grain oriented Laves phase compounds of Tb{sub x}Dy{sub 1-x}Fe{sub 2}. The magnetostrains observed in the oriented compounds, though containing {approx}20% porosity as presently prepared, are far superior to those of arc cast and highly dense liquid phase sintered materials. Also, it is shown that the alignment achieved is strongly dependent on the Tb/Dy ratio.
Date: October 1, 1977
Creator: Malekzadeh, M. & Pickus, M.R.
Partner: UNT Libraries Government Documents Department

THE EFFECT OF MAGNETICALLY ALIGNED POWDER ON THE MAGNETOSTRICTION OF SINTERED RARE EARTH-IRON LAVES PHASE COMPOUNDS

Description: A powder metallurgical approach is utilized to prepare grain oriented Laves phase compounds of Tb{sub x}Dy{sub 1-x}Fe{sub 2}. The magnetostrains observed in the oriented compounds, though containing {approx}20% porosity as presently prepared, are far superior to those of arc cast and highly dense liquid phase sintered materials. Also, it is shown that the alignment achieved is strongly dependent on the Tb/Dy ratio.
Date: October 1, 1977
Creator: Malekzadeh, M. & Pickus, M.R.
Partner: UNT Libraries Government Documents Department

FLUID DYNAMICS MODEL FOR SALT-DOME EVOLUTION

Description: A fluid dynamics model for the evolution of salt domes and ridges is presented. The model assumes a rigid substrate, finite thickness of both strata with no slip and a rigid or free surface of overburden. Inertial terms in the Navier-Stokes equations are neglected due to the large viscosities considered and the initial perturbation is taken to be sinusoidal. Finite sine and cosine transforms are used to solve the flow equations and the resulting systems of equations reproduces the velocity field equation of Ramberg's model. Assuming an initial interface, the infinite series solution is truncated to obtain the constants of the integration from the boundary conditions. The interface is then moved to a new position. Thus, the new shape for the interface can be traced for any time. For small perturbations, we obtain results that are approximately those obtained by the linear theory. Results of the numerical solution of the model for both large and small perturbations are presented.
Date: August 1, 1977
Creator: Nasir, N. E. & Dabbousi, O. B.
Partner: UNT Libraries Government Documents Department

THE TEMPERATURE-DEPENDENT SURFACE STRUCTURE, COMPOSITION AND ELECTRONIC PROPERTIES OF THE CLEAN SrTiO3(111) CRYSTAL FACE: LEED, AES, ELS AND UPS STUDIES

Description: Low-energy-electron diffraction, Auger-electron spectroscopy, electron-energy-loss, and ultraviolet-photoelectron spectroscopies were used to study the structure, composition, and electron energy distribution of a clean single-crystal (111) face of strontium titanate (perovskite). The dependence of the surface chemical composition on the temperature has been observed along with corresponding changes in the surface electronic properties. High-temperature Ar-ion bombardment causes an irreversible change in the surface structure, stoichiometry, and electron energy distribution. In contrast to the TiO{sub 2} surface, there are always significant concentrations of Ti{sup 3+} in an annealed ordered SrTiO{sub 3} (111) surface. This stable active Ti{sup 3+} monolayer on top of a substrate with large surface dipole potential makes SrTiO{sub 3} superior to TiO{sub 2} when used as a photoanode in the photoelectrochemical cell.
Date: December 1, 1977
Creator: Lo, Wei Jen & Somorjai, G. A.
Partner: UNT Libraries Government Documents Department

TEMPERATURE INDEPENDENCE OF THE ANGLE-RESOLVED X-RAY PHOTOEMISSION SPECTRA OF GOLD AND PLATINUM VALENCE BANDS

Description: Angle-resolved valence-band x-ray photoemission spectra were taken along the [111] and [100] directions of gold single crystals and along the [100] direction of a platinum single crystal at room temperature (293K) and on a probe cooled nearly to liquid nitrogen temperature (77K). No change was detected on cooling the samples, in contrast to expectations based on a simple direct-transition model. A simple 'matrix-element' model appears to predict spectra well even at low temperatures, perhaps because the complexity of the high-energy final-state bands permits sampling effectively throughout the zone.
Date: September 1, 1977
Creator: Dabbousi, O. B.; Wehner, P.S. & Shirley, D.A.
Partner: UNT Libraries Government Documents Department

THERMODYNAMICS OF ELECTROLYTES. X. ENTHALPY AND THE EFFECT OF TEMPERATURE ON THE ACTIVITY COEFFICIENTS.

Description: Heat of dilution and of solution data are fitted to the form of equation corresponding to that used successfully for activity and osmotic coefficients over a wide range of concentration. The resulting parameters give the change with temperature of the activity and osmotic coefficients. Results are reported for 84 electrolytes of 1-1, 2-1, 3-1, and 2-2 valence types.
Date: November 1, 1977
Creator: Silvester, Leonard F. & Pitzer, Kenneth S.
Partner: UNT Libraries Government Documents Department

THERMODYNAMICS OF ELECTROLYTES. XI. PROPERTIES OF 3-2, 4-2, AND OTHER HIGH-VALENCE TYPES

Description: Various thermodynamic properties are considered for very high-valence 3-2 and 4-2 electrolytes in water at room temperature. These solutions show the behavior described by Davies in which ion pairing arises as the concentration increases follow by re-dissociation at still higher concentrations. Heat of dilution data, which extend below 10{sup -4} M, are interpreted with the same form of equation used earlier for 2-2 electrolytes. Activity and osmotic coefficient data do not extend to low enough concentration for independent, interpretation, but they are treated with the aid of conductance data in the more dilute range. Parameters are reported for A{ell}{sub 2}(SO{sub 4}){sub 3}, La{sub 2}(SO{sub 4}){sub 3}, In{sub 2}(SO{sub 4}){sub 3}, and several cyanoferrates. High-valence electrolytes show a special behavior at very low concentrations which was recognized by Bjerrum who showed in 1926 that purely electrostatic forces would yield an ion association. Davies showed that this association commonly reached a maximum at an intermediate concentration above which there was a re-dissociation. From one viewpoint, this ion association is an artifact of the linearization approximation in the Debye-Hueckel theory since a more exact statistical treatment yields agreement with experiment without assuming a separate associated species. If an association equilibrium is assumed for these electrolytes, it is found that the value of the association constant depends on the assumptions about the activity coefficients of the ions. To the extent that these effects are important for 2-2 electrolytes, they are discussed in paper III{sup 6} of this series. While in 3-2 and 4-2 electrolytes the effects are of the same nature as those in the 2-2 solutes, they occur at much lower concentration in the higher-valence solutes; consequently new problems arise in treating experimental data. Indeed, it is only the conductance and heat-of-dilution measurements, which extend down to 10{sup -5} M, that show clearly ...
Date: December 1, 1977
Creator: Pitzer, Kenneth S. & Silvester, Leonard F.
Partner: UNT Libraries Government Documents Department

THE STRUCTURE OF GRAIN BOUNDARIES IN SILICON NITRIDE BASED ALLOYS

Description: Grain boundaries in silicon-based ceramics have been characterized by high resolution electron microscopy including the technique of lattice fringe imaging, and this work is illustrated with examples from both hot-pressed silicon nitrides (MgO and Y{sub 2}O{sub 3} fluxed) and a magnesium-sialon (Mg{sub 1.86} Si{sub 1.67} Al{sub 2.47} O{sub 3.19} N{sub 3.81}). Room temperature observations of the glassy phase are consistent with it being only a partially wetting phase, indicating that it cannot form a continuous film. The atomic configuration of the grain boundaries in both materials is presented together with lattice fringe observations of segregation at grain boundaries in the magnesium-sialon.
Date: December 1, 1977
Creator: Clarke, David R. & Thomas, G.
Partner: UNT Libraries Government Documents Department

QUANTUM MECHANICAL REACTIVE SCATTERING VIA EXCHANGE KERNELS: APPLICATION TO THE COLLINEAR H+H2 REACTION

Description: A formulation of quantum mechanical reactive scattering given by Miller is applied to the collinear H + H{sub 2} reaction. The approach is the direct analog to the Hartree-Fock method of electronic structure theory, and it obviates the need for specialized (e.g., 'natural' collision) coordinates. The rearrangement process takes place via an explicit exchange interaction (cf. electron exchange in Hartree-Fock theory), and closed channels are incorporated via a square-integrable set of correlation functions. Agreement with results obtained by others using other methods is excellent, showing this approach to quantum mechanical reactive scattering to be a viable one.
Date: October 1, 1977
Creator: Garrett, Bruce G. & Miller, William H.
Partner: UNT Libraries Government Documents Department

THE 3d2 - 3d4f TRANSITIONS IN V IV

Description: The 3d4f levels in the spectrum of triply ionized vanadium, V IV, were located by L. Iglesias. She located these levels by identifying transitions from the 3d{sup 2} ground configuration to the 3d4p levels, then to the 3d4d levels and finally to the 3d4f levels. She also identified the transitions from the 3d4d levels to the 3d5p levels, continued up to the 3d5d levels, then back down to the 3d4f levels. Though the 3d4f levels were well established by two routes, the direct transitions from the ground state were not observed, being beyond her experimental range which stopped at 675 {angstrom}. We have photographed the spectrum of vanadium in the region of 190-650 {angstrom} and the direct transitions from 3d{sup 2} to 3d4f have been observed. The spectrum was excited with a vacuum sliding-spark discharge between vanadium metal electrodes separated by a quartz spacer as described previously. Peak discharge current was 1000 {angstrom}. The spectrum was photographed on Kodak SWR plates using the 10 {center_dot} 7 m grazing incidence spectrograph at the National Bureau of Standards in Washington, D.C. The plate factor in the region of interest is about 0.27 {angstrom}/mm. The plates were measured on a Grant comparator. Lines of yttrium IV and V, oxygen III and carbon IV were used for reference standards. The same plates were used to obtain the spectrum of vanadium V as reported previously by van Deurzen. Table I contains 19 transitions from the ground configuration, 3d{sup 2}, to the 3d4f configuration and 3 transitions from the ground configuration to the 3dSp configuration. Column 1 in the table is our measured vacuum wavelengths. The intensities in column 2 are visual estimates on a scale of 0 to 9. Column 3 lists the wavenumber of the measured lines. The classifications of the transitions and the ...
Date: September 1, 1977
Creator: Shalimoff, G. V. & Conway, J.G.
Partner: UNT Libraries Government Documents Department

PREPARATION AND PROPERTIES OF THE ACTINIDE BOROHYDRIDES: Pa(BH4)4, Np(BH4)4, AND Pu(BH4)4

Description: The actinide borohydrides, Pa(BH{sub 4}){sub 4}, Np(BH{sub 4}){sub 4}, and Pu(BH{sub 4}){sub 4} have been synthesized. Pa(BH{sub 4}){sub 4}, a solid at 20{sup o} is isostructural with U(BH{sub 4}){sub 4}. Np(BH{sub 4}){sub 4} and Pu(BH{sub 4}){sub 4} are volatile liquids at 20{sup o} but are isostructural at low temperatures and crystallize in a tetragonal crystal structure type. The metal atom distances indicate the solid is monomeric and similar to Zr(BH{sub 4}){sub 4}. Preliminary Raman spectra on solid Np(BH{sub 4}){sub 4} support this idea. Gas-phase infrared spectra indicate theNp and Pu atoms in these compounds are surrounded by four BH{sub 4}{sup -} groups in a tetrahedral array with each B coordinated via 3 hyrodgen bridge bonds to the metal atom.
Date: October 1, 1977
Creator: Banks, R.H; Edelstein, N.M; Rietz, R.R.; Templeton, David H. & Zalkin, Allan
Partner: UNT Libraries Government Documents Department

ON THE EFFECT OF PRIOR AUSTENITE GRAIN SIZE ON NEAR-THRESHOLD FATIGUE CRACK GROWTH

Description: It is generally accepted that the fatigue or endurance strength of planar slip materials, such as steel and brass, is increased by refining the grain size, whereas in wavy slip materials, such as pure copper and pure aluminum, the fatigue strength is unaffected. However, there is little similar evidence of an effect of grain size on fatigue crack propagation. In both wavy and planar slip metals, growth rates appear independent of grain size. For example, variations in grain size from 10 to 200{micro}m in 70/30 brass (6), and from 45 to 480{micro}m in austenitic stainless steel produce no measurable change in fatigue crack propagation rates over a range of growth rates from 10{sup -5} to 10{sup -2} mm/cycle. Recently, however, there have been indications in the literature that grain size may indeed influence crack propagation behavior at growth rates less than 10{sup -5} to 10{sup -6} mm/cycle approaching the threshold for crack propagation, {Delta}K{sub 0}. Robinson and Beevers report an order of magnitude decrease in near-threshold growth rates in {alpha}-titanium after coarsening the grain size from 20 to 200{micro}m. Similar effects have been seen in Ti-6Al-4V. Furthermore, Masounave and BaIlon have observed a marked increase in threshold {Delta}K{sub 0} values in a range of low strength steels by increasing ferrite grain size. In all the above studies however, no attempt was made to control strength; and the effect of coarsening the grain size may well have been caused by a concurrent decrease in material strength, particularly since it is known that, in steels at least, near-threshold fatigue crack growth is markedly decreased by reducing the yield strength. A comparison at constant yield strength between coarse and fine-grained materials has been made in ultra-high strength steel (300-M) where it was found that, on enlarging the (prior austenite) grain size from 20 ...
Date: January 1, 1977
Creator: Carlson, M.F. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

D-ORBITAL DIRECTED PHOTOEMISSION FROM MANGANESE FLUORIDE SINGLE CRYSTALS USING A1Kalpha RADIATION

Description: Angle-resolved photoemission energy distributions (PED's) were obtained from valence bands of MnF{sub 2} single crystals using AlK{alpha} radiation. A pronounced variation in the PED's was observed as the electron take-off angle was varied relative to the crystalline axes, for the (111) crystal face. The observed variation is attributed to the t{sub 2g} and e{sub g} symmetry properties of the manganese 3d initial state wave functions and is well described by an angle-dependent transition-matrix model. The results are in good agreement with the multi-configurational Hartree-Fock calculations of Viinikka and Bagus.
Date: September 1, 1977
Creator: Sherwood, P.M.A.; McFeely, F.R.; Kowalczyk, S.P. & Shirley, D.A.
Partner: UNT Libraries Government Documents Department

CORROSION OF Fe-10Al-Cr ALLOYS BY COAL CHAR

Description: Corrosion of iron-base alloys at 982 C (1800 F) by coal char is observed and the phase morphologies discussed. No sulfidation was observed at 50 hours exposure. After 100 hours, internal aluminum-rich sulfides were observed along with thick outer scales of iron oxide. The species causing the high-temperature induced corrosion are probably sulfides and sulfates, present in most coal chars. Possible mechanisms for the corrosion are also discussed.
Date: October 1, 1977
Creator: Gordon, B.A. & Nagarajan, V.
Partner: UNT Libraries Government Documents Department

CURRENT RESEARCH TOWARDS IMAGING BIOLOGICAL MOLECULES USING FIELD DESORPTION MICROSCOPY AND FIELD ION MICROSCOPY OF DIAMOND

Description: Work is currently in progress investigating the possibility of imaging large organic and biological molecules in a modification of field desorption microscopy (FDM). A field ion microscope (FIM) is being converted to an FDM by installation of a chevron channel tron electron multiplier array (CEMA), commonly called a chevron channel plate. The chevron CEMA has a gain of over 10{sup 7} and can thus produce enough light from single field desorbed ions to be readily photographed. In field desorption microscopy, a fine metal tip is subjected to positive electric fields high enough to field evaporate the metal as positive ions. These ions follow the field lines radially away from the tip and strike the CEMA. One therefore gets a greatly magnified image of the tip by field evaporated ions. The magnification, M equals R/{beta}r where R is the tip to screen distance, typically 5-10 cm, r is the tip radius, typically 100-1000 {angstrom} and {beta} is an electrostatic compression factor due to the field lines being Slightly compressed at the tip. Magnifications of over 10{sup 6} are easily obtained and at low temperatures, metal atoms field evaporating from adjacent lattice positions on the tip will strike the CEMA within separate areas. Therefore the resolution is less than 3 {angstrom}. A large amount of work has been done attempting to image molecules on tips by FIM and field emission microscopy (FEM). In FEM, the resolution is normally limited to about 25{angstrom} due to the large transverse momentum of the emitted electrons. The images of molecules obtained have therefore been of low resolution and hard to interpret due to effects which are still controversial in interpretation. By reversing the field and adding an imaging gas one would hope to be able to get high resolution FIM images of adsorbed molecules. It turns ...
Date: November 1, 1977
Creator: Hirsch, G. & Washburn, J.
Partner: UNT Libraries Government Documents Department

DEOTERIUM MAGNETIC RESONANCE OF SOME POLYMORPHIC LIQUID CRYSTALS: THE CONFORMATION OF THE ALIPHATIC END CHAINS

Description: Deuterium magnetic resonance measurements of four members of the homologous series p-alkoxybenzylidene-p-alkylaniline (no {center_dot} m), perdeuterated in their alkoxy chains, are reported. The compounds studied were 40 {center_dot} 7, 50 {center_dot} 7, 60 {center_dot} 7 and 70 {center_dot} 7. For 50 {center_dot} 7 various isotopic species specifically deuterated in the alkoxy chains, as well as in the benzylidine moiety, were prepared and their DMR studied. These measurements allowed a complete assignment of the resonances from the alkoxy chain. The spectrum of all four compounds was studied over their whole mesomorphic regions. In most phases well resolved spectra were obtained yielding the various quadrupole splittings and in many cases also the dipolar interactions within the methylene and methyl groups. Using double quantum spectroscopy dipolar splitting between different methylene deuterons could also be resolved. The methylene quadrupolar splittings and the dipolar interaction within the methylene groups decrease along the chain towards the methyl end in a characteristic stepwise manner. This behavior is attributed to chain reorientational freedom and is quantitatively interpreted in terms of two structural factors: (i) Fast dynamical equilibrium between the all-trans conformation of the alkoxy chains and chain conformations involving one or more kinks, and (ii) A molecular model in which the aliphatic chain axis is inclined with respect to the molecular long axis. The characteristic pattern of the splitting can then be reproduced by assuming a monotonically increasing kink probabilities along the chain towards its methyl end. This interpretation is used to estimate the kink probability distribution in the alkoxy chains in the various compounds and mesophases. No significant effect of the mesophase structure on the kink statistics was found.
Date: October 1, 1977
Creator: Hsi, Shan; Zimmermann, Herbert & Luz, Zeev
Partner: UNT Libraries Government Documents Department