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High resolution, proton decoupled {sup 13}C nmr are observed for a series of neat nematic liquid crystals, the p-alkoxyazoxybenzenes, and a smectic-A liquid crystal, diethylazoxydibenzoate in a magnetic field of 23 kG. The (uniaxial) order parameters S = <P{sub 2}(cos{theta})> are found to be about 0.4 and 0.9 for the nematic and smectic-A phase respectively at the clearing points. The order parameter increases with decreasing temperature in the nematic phase but is constant, or nearly so, with temperature in the smectic-A phase. In the nematic series studied, the ordering exhibits an even-odd alternation along the series and qualitative agreement with a recent theory due to Marcelja is found. In both phases, the spectra show that the molecule rotates rapidly about its long axis. Tentative conclusions about molecular conformational motion and {sup 14}N spin relaxation are presented for both nematic and smectic-A phases. In the smectic-A phase, the sample is rotated about an axis perpendicular to H{sub 0} and the resulting spectra are discussed. The theory of observed chemical shifts in liquid crystals is treated in an appendix. Equations are derived which relate the nmr spectra of liquid-crystals to the order parameters. A model for the smectic-C phase due to Luz …

A search for innovative synthetic routes to new metal-metal bonded metal-halide clusters resulted in isolation of two completely independent dimeric species. The syntheses and characterizations of Ta/sub 2/X/sub 6/(SC/sub 4/H/sub 8/)/sub 3/ (X = Cl, Br) and ((n-C/sub 3/H/sub 7/)/sub 4/N)/sub 2/(W/sub 2/Br/sub 9/) followed entirely different experimental routes, yet occasionally similar properties linked the two projects. (auth)

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The design of a crossed molecular beam ''supermachine'' for neutral-- neutral collisions is discussed. The universal electron bombardment ionizer, mass filter, and ion detection system of the detector, the supersonic nozzle sources, the differential pumping arrangement for the sources and detector, the time-of-flight detection of scattered products, and the overall configuration of the apparatus are described. The elastic scattering of two systems, CH$sub 4$ + Ar and NH$sub 3$ + Ar, has been measured using the supermachine with two supersonic nozzle sources. The rainbow structure and the interference oscillations are seen in each system. The best fit to the data was found using a Morse--Spline--Van der Waals (MSV) potential. The three potential parameters epsilon, r/sub m/, and $beta$ were found to be 2.20(+-0.04) x 10$sup -14$ ergs, 3.82(+-0.04)A, and 7.05 +- 0.20 for CH$sub 4$ + Ar, and 2.21(+-0.04) x 10$sup - 14$ ergs 3.93 (+-0.05)A, and 8.45 +- 0.30 for NH$sub 3$ + Ar. A new phenomenon in crossed molecular beams of condensation of a molecule on a cluster to form a complex was observed. A bromine molecule condensed on clusters of chlorine (Cl$sub 2$)/sub chi/ and ammonia (NH$sub 3$)/sub chi/. The value of chi for measurements in these …

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In order to test a collisional pumping model as a mechanism for cooling the 6 cm and 2 cm doublets of interstellar formaldehyde, a quantum mechanical scattering calculation is performed. To obtain the intermolecular interaction between H$sub 2$CO($sup 1$A$sub 1$) and He($sup 1$S) two calculations are performed, a Hartree-Fock (HF) potential surface and a configuration interaction (CI) surface. A basis set of better than ''triple zeta plus polarization'' quality is used to compute the HF portion of the potential energy surface. This portion is highly anisotropic and has a slight attraction arising from induction effects at intermolecular separations around 9 a.u. The HF surface is modified through a series of CI calculations. Correlation is found to have little effect in the strongly anisotropic repulsive region of the interaction potential but dominates the well and long-range regions. The maximum well depth is attained for in-plane approaches of He and lies in the range 35-40$sup 0$K for arbitrary theta at center of mass separation of 7.5 a.u. The entire surface is fit to a spherical harmonic expansion to facilitate scattering applications. (auth)

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Optical properties of Nb alloys were investigated. Calorimetric measurements of absorptivity between 0.2 and 5.5 eV were taken for Nb samples with 20, 50, and 80 percent Mo and for Nb samples containing 10 percent Zr, 20 percent V, and 20 percent Ta. Reflectivity data for two of these samples in the ultraviolet region and known reflectivities for the pure metals to 35 eV provided the basis for extrapolation to high energies. The data were Kramers--Kronig analyzed to determine the dielectric function. The structure is discussed in terms of interband transitions as predicted by a rigid band model for the NbMo alloys. (auth)

A variant of the maraging class of steels is proposed for application at 77$sup 0$K and below where a combination of very high strength and good toughness is required. The alloy has a composition of Fe-12Ni-4Co-2Mo-0.05Ti where low interstitial content. The as quenched and quenched and aged structures were completely martensitic with a prior austenitic grain size of 10 to 12 $mu$m. This structure had a Y.S. of 138.5 ksi and 154 ksi before and after aging respectively. All aging was done at 444$sup 0$C for 4 hours. The DBTT was shown to lie above 77$sup 0$K as measured by C/sub v/ testing. Based on dilatometric studies of the $alpha$ $Yields$ $gamma$ and $gamma$ $Yields$ $alpha$ transformation temperatures a cycling treatment consisting of reportedly heating to above the A/sub f/ temperature followed by a water quench was utilized to further reduce the prior $gamma$ grain size to approximately 4 to 6 $mu$m. The structure was completely martensitic and possessed a Y.S. of 151 ksi at 77$sup 0$K in the unaged condition with a Y.S./K/sub IC/ ratio of 1.9 while the aged structure showed a Y.S. of 162 ksi with a Y.S./K/sub IC/ ratio of 1.3. C/sub v/ testing showed the …

Time-differential perturbed angular correlation techniques were applied to a systematic study of insulating antiferromagnets and rare-earth intermetallic alloys doped with either /sup 111m/Cd or $sup 111$In. The internal magnetic fields and electric field gradients at the radioactive nucleus are deduced from the experimentally measured perturbation factors. The analysis of fluoride, chloride, oxide, and sulfide data shows the systematic variation of the observed supertransferred hyperfine fields with the intervening anion covalency and allows extraction of covalency parameters after the adoption of a simple model. A comparison of the transferred hyperfine field data between fluoride perovskites and the corresponding quadratic layer compounds produces a value for the zero- point spin deviation in magnetically two-dimensional antiferromagnets which is in qualitative agreement with existing theoretical estimates. Paramagnetic shifts due to transferred hyperfine field and field-induced spin-flopping have also been observed. By careful temperature regulation the temperature dependence of the sublattice magnetization can be plotted next to a diamagnetic impurity in RbMnF$sub 3$ and MnF$sub 2$. A shift in the transferred hyperfine field at Cd doped into MnS has been measured under the application of moderate pressures up to 22 kbar. Analysis of the electric field gradients at the In and Sn sites in the …