Microwave spectrum,structure and dipole moment of trimethylamine-borane

The ground state rotational spectra often isotopic species of trimethylamineborane, (CH₃)₃N¹⁰BH₃, (CH₃)₃N¹¹BH₃, (CH₃)₃N¹⁰BD₃, (CH₃)₃N¹¹BD₃, (CH₃)₃N¹¹BD₂H, (CD₃)₃N¹⁰BH₃, (CD₃)₃N¹¹BH₃, (CD₃)₃N¹⁰BD₃, (CD₃)₃N¹¹BD₃ and (¹³CH₃)(¹²CH₃)₂N¹¹BH₃, have been measured and the effective moments of inertia obtained. The utilization of Kraitchman's equations leads to an r_s value of the B-H distance of 1.211±0.003 Å and a NBH angle of 105.32±0.16°. By a least squares fit of the rotational constants the following structural parameters were obtained: r(NC) = 1.495 Å, r(BN) = 1.609 Å, and ∠BNC = 110.9°. The value of the dipole moment was found to be 4.59±0.13 D. A lower limit to the barrier to internal rotation of the BH₃ group was determined to be 3.4 kcal/mole.     

Control of density fluctuations and electron transport in the reversed-field pinch

Contrary to what has been observed thus far collision-induced light scattering (CILS) can be completely polarized. This exceptional behavior characterizes the very far wing of the binary CILS spectrum by gaseous helium. This conclusion is drawn from an experimental study of the depolarization ratio of He (2) in a much extended, previously unexplored, spectral domain. Our analysis shows that this property, unique thus far, is mainly due to an almost perfect cancellation between polarization and exchange pair polarizability contributions to the depolarized spectrum, taking place at internuclear distances shorter than the atomic diameter.     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

Qualitative properties of modified equations

Suppose that a consistent one-step numerical method of orderr is applied to a smooth system of ordinary differential equations.Given any integer m 1, the method may be shown to be of orderr + m as an approximation to a certain modified equation. Ifthe method and the system have a particular qualitative propertythen it is important to determine whether the modified equationsinherit this property. In this article, a technique is introducedfor proving that the modified equations inherit qualitativeproperties from the method and the underlying system. The techniqueuses a straightforward contradiction argument applicable toarbitrary one-step methods and does not rely on the detailedstructure of associated power series expansions. Hence the conclusionsapply, but are not restricted, to the case of Runge-Kutte methods.The new approach unifies and extends results of this type thathave been derived by other means: results are presented forintegral preservation, reversibility, inheritance of fixed points.Hamiltonian problems and volume preservation. The techniquealso applies when the system has an integral that the methodpreserves not exactly, but to order greater than r. Finally,a negative result is obtained by considering a gradient systemand gradient numerical method possessing a global property thatis not shared by the associated modified equations.     

Flux line lattice symmetries in the borocarbide superconductor LuNi2B2C

We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor LuNi₂B₂C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field. H ₂(T), rises sharply, bending away from H _c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H _tr=3–3.5 kOe. Below H _tr the FLL nearest neighbor direction is parallel to the b-axis, and above H _tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model.     

Synthesis and hydroamination catalysis with 3-aryl substituted pyrrolyl and dipyrrolylmethane titanium(IV) complexes

Using an iridium-catalyzed borylation/Suzuki-Miyaura coupling sequence several 3-aryl-pyrroles were accessed; in addition, dipyrrolylmethanes incorporating these 3-arylpyrroles were synthesized. Using the monodentate pyrrolyls, Ti(NMe(2))(2)(HNMe(2))(pyr(3,5-CF3))(2) (1) and a 2,4-diarylpyrrolyl complex Ti(NMe(2))(3)(pyr(Ar/Ar')) (2) were prepared and structurally characterized. Titanium species bearing the new dipyrrolylmethane ligands Ti(NMe(2))(2)(NHMe(2))(dpm(3,5-CF3)) (3) and Ti(NMe(2))(2)(NHMe(2))(dpm(F3)) (4) were also generated. Kinetics under pseudo-first order conditions with 3 and 4 showed them to be measurably more active than the parent derivative without the electron-withdrawing aryl groups.     

Synthesis,characterization and vibrational investigation of divinylborinic anhydride

The new molecule divinylborinic anhydride [(CH₂CH)₂B]₂O as been prepared by the limited hydrolysis of divinylchloroborane. Characterization of the compound has included the preparation of 1 : 1 adducts with trimethylphosphine, dimethylphosphine and trimethylamine. Born-11 and carbon-13 NMR spectra have been obtained and have been interpreted in terms of mesomeric interactions between the empty boron pπ orbital and unshared pairs of electrons on oxygen as well as the pi electron system of the vinyl moiety. The Raman spectra (3500–200 cm^-1) of liquid and solid [(C₂H₃)₂B]₂O and the infrared spectra (3500–200 cm^-1) of gaseous and solid [(C₂H₃)₂B]₂O ¹ have been investigated for both the ¹⁶O and ¹⁸O isotopic species. The vibrational data indicate that the molecule possesses C₁ symmetry and a linear BOB angle.