Kondo effect in a double quantum-dot molecule under the effect of an electric and magnetic field

Electron tunneling through a double quantum-dot molecule, in the Kondo regime, under the effect of a magnetic field and an applied voltage, is studied. This system possesses a complex response to the applied fields characterized by a tristable solution for the conductance. The different nature of the solutions are studied in and out thermodynamical equilibrium. It is shown that the interdot coupling and the fields can be used to control the region of multistability. The mean-field slave-boson formalism is used to obtain the solution for the problem.     

Acoustic fluid flow through holes and permeability of perforated walls

We first study the unsteady incompressible fluid flow through a hole in a wall in the two- and three-dimensional cases. In the first case, a convolution relation is obtained between the fluid flux through the hole and the difference of pressure between the far regions on the two sides of the wall. In the two-dimensional case, the pressure increases logarithmically with distance from the wall. In a second part, we study acoustic flow in a domain containing a wall with many small holes. The distance between two contiguous holes is of order η and the size of each hole, ε (η and ε are two small parameters). In the three-dimensional case the critical behaviour appears for ε = η²: it is described by a convolution relation between the flow through the wall and the jump of pressure. In the two-dimensional case, the critical behaviour appears if η log ε tends to a constant; there is a differential relation between the flow through the wall and the jump of pressure.     

Das Schwingungsspektrum des synthetischen Carnotits

The infrared and laser-Raman spectra of synthetic carnotite, K₂[(UO₂)₂V₂O₈], are reported and discussed. Force constants for the terminal V-O bonds as well as for the UO₂ ²⁺ ions are evaluated. From the spectroscopic data, a U-O bond length of 1.81 Å is estimated for the uranyl ion in this compound.

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15. Mitteilung der Reihe Orthovanadate und verwandte Verbindungen 14. Mitt:E. J. Baran, J. C. Pedregosa undP. J. Aymonino, Mh. Chem.106 1085 (1975).     

Synthesis of substituted 1-benzyl-2,4,6-triphenyl-2,3-dihydro-pyrazolo [3,4-b] [1,4]diazepines

The acid catalyzed condensation of 4,5-diaminopyrazoles and chalcones gave the hitherto unknown 1-benzyl-2,4,6-triphenyl-2,3-dihydropyrazolo[3,4-b][1,4]diazepines derivatives. The structure of all products was supported by ir, ¹H and ¹³C-nmr and mass spectra.     

Exciton localization in a Pt-acetylide complex

We present a theoretical study of the low-lying electronic excitations in the [Pt(P((n)Bu)(3))(2)(ethynylbenzene)(2)] molecule. Although the ground electronic state possesses D(2)(h) symmetry, with both ethynylbenzene ligands being equivalent, in the excited state the molecule breaks the symmetry deforming along a b(3u) direction and localizing the excitation on a single ligand. This localized exciton is of (3)pipi* nature with the unpaired electron and hole spread over one of the benzene rings and the ethyne linkage. The localization indicates an activated hopping mechanism for transport. Our estimate of the barrier is approximately 0.61 eV.     

Mittlere Schwingungsamplituden und thermodynamische Funktionen von TeF5Cl

Mean amplitudes of vibration and thermodynamic functions of TeF₅Cl have been calculated in a wide temperature range, using known spectroscopic data. The results are briefly discussed and comparisons with some related species are made.     

Evidence for different types of water participation in the solvolysis of 1-adamantyl, tert-butyl, and methyl chlorides from density functional theory computations

[structure: see text] The activation energy in the gas phase (deltaE(double dagger)) and the free energy of activation (deltaG(double dagger)) in water solution for the hydrolysis of the monohydrates of methyl chloride (MeCl), tert-butyl chloride (t-BuCl), and 1-adamantyl chloride (AdCl) have been computed with the B3LYP/631-G(d) method and the polarizable continuum (PCM) solvation model. There is a fair agreement between the deltaG(double dagger) values computed by us and the experimental data. The mechanistic implications of our computations are in severe contradiction with conventional representations. Thus, the computed nucleophilic solvent assistance (NSA) for the backside attack of a water molecule in the hydrolysis of MeCl is slightly lower than the corresponding NSA for t-BuCl. Hence, the hydrolysis of both MeCl and t-BuCl takes place mainly according to the classical S(N)2 mechanism. The most relevant difference is that deltaG(double dagger) for the frontside attack of water to t-BuCl is disfavored only by ca. 2 kcal/mol with regard to the backside attack but by ca. 23 kcal/mol in the case of MeCl. The higher solvolysis rate in water of t-BuCl in relation to AdCl is not due to steric factors affecting the specific solvation of the corresponding transition states, but to differential bulk solvent effects, which are accounted for by the PCM model.     

Determination of the preferred tautomeric form of 4-nitrohistidine

Spectrophotometric pKa determinations of methyl derivatives of N^α-acetyl-4-nitrohistidine methyl ester 1 have been used to determine the position of the tautomeric equilibrium of 1 . The N₁-H tautomer is the predominant form with an equilibrium constant K_T of 48. The conclusion is supported qualitatively by the study of ¹H-nmr and ¹³C-nmr chemical shifts of the imidazole ring atoms and their changes from neutral to acidic media.     

A novel [2 + 2 + 1]/[2 + 1] tandem cycloaddition reaction of Fischer alkynyl carbenes with strained bicyclic olefins

The reaction of strained bicyclic olefins with alkynyl carbenes and terminal olefins involves the creation of five new sigma C-C bonds with the concomitant formation of two new rings, thus creating a complex and densely functionalized structure in a single operation.