Magnetic structure,phase diagram,and a new type of spin-flop transition dominated by higher order interaction in a localized 5f system U3Pd20Si6

The magnetic structure of the localized-5f uranium intermetallic compound U3Pd20Si6 has been determined by means of a neutron diffraction experiment. Our data demonstrate that this compound has a collinear coupling of the sublattice ordering of the uranium spins on the 4a and 8c sites. We conclude that higher-order exchange and/or quadrupole interactions are necessary to stabilize this unique collinear structure. We discovered a new type of spin-flop transition against the uniaxial anisotropy induced by this collinear coupling.     

Investigation of intramolecular sulfur-nitro interactions in 2-(2′-pyridylthio)-3-nitropyridine by 13C-NMR spectroscopy and x-ray crystallography

The single crystal X-ray diffraction structure of 2-(2′-pyridylthio)-3-nitropyridine is reported. A non-bonded interaction was observed between the sulfur atom and one of the oxygen atoms of the nitro group with an interatomic distance of 2.678 A. Examination of the molecule's behavior in solution by ¹³C-nmr spin-lattice (T₁) relaxation measurements showed the non-nitro bearing pyridyl ring to reorient anisotropically about the C2′-C5′ bond axis. In contrast, the nitro substituted pyridine ring did not appear to exhibit anisotropic reorientation about the corresponding C2-C5 bond axis. Rather, approximately equivalent relaxation times were noted for all protonated ring carbons, indicating that the relaxations of this portion of the molecule were governed by the overall isotropic reorientation of the system. Based on these observations, it was concluded that the intramolecular sulfur-nitro interaction also operates in the solution state and is sufficiently strong to prevent free rotation of the substituted portion of the molecule about the C2-S bond axis.     

Energy and angular differential cross sections for K + NO2 charge transfer reactions

Doubly differential cross sections, in energy and angle, are reported for the electron transfer reaction between potassium and nitrogen dioxide in a crossed beam apparatus at relative collision energies between 2.7 and 30.8 eV. The formation of NO^?₂ in its ground ¹A₁ and excited ³B₁ state has been observed. Theoretical consideration of these processes indicates that bond bending during the collision has a stronger influence on ion-pair formation than bond stretching. At the lower collision energies most of the excess energy is converted into internal energy of NO^?₂.     

Theory of excluded volume effects in nematic liquid crystals

An expression for the free energy of nematic liquid crystals is given by taking account of the excluded volume effects as well as dispersion forces. The dependence of nematic order on concentration and/or shape of molecules is discussed.     

Infrared intensities of the fundamental vibrations of liquid H2O

Infrared absorption intensities of the fundamental vibrations of liquid H₂O have been obtained by measuring transmissions at two sample thicknesses (about 9 and 0.9 μ). The effect of multiple internal reflections on the observed absorptions is examined in terms of thin-film optics. It is shown that this simple method yields precise absorption intensities, without corrections for the effects of multiple internal reflections. The resulting intensities are 89.9 × 10³ cm/mmol and 5.91 × 10³ cm/mmol for the stretching and bending vibrations, respectively. The latter value was estimated after eliminating the absorption of intermolecular vibrations from the 1400–2400 cm^-1 region by means of computer simulation.     

Vacuum UV photoelectron intensity of gaseous compounds: I. HeI spectra of simple compounds

A new method for determining absolute photoionization cross sections for gaseous compounds is proposed. In this method a mixture of a sample and a standard gas (N₂) is used in photoelectron intensity measurements so that the relative intensity of the component is obtained with respect to N₂ The relative photoelectron band area is converted to the absolute photoionization cross section on the basis of the absolute cross-section data of N₂ recently reported by Samson et al. This method has been applied to various aliphatic compounds to study the effect of alkyl substitution on photoionization cross sections of O- and N-nonbonding electrons for 584-Å radiation.