The N2 problem in molecular CI calculations

The possible existence of spurious terms increasing as the square of the number of electrons is theoretically proved for the CI treatments of molecules limited to single and double excitations, and is revealed by some numerical calculations (alcanes and juxtaposed hydrogen molecules). An improved perturbation scheme is suggested in order to evaluate the CI energy lowering more carefully. Covergence difficulties are found for larger systems (benzene).     

Hyperfine interaction of 181Ta in chromium

The hyperfine interaction of ¹⁸¹Ta diluted in chromium has been measured as a function of temperature by time-differential perturbed angular correlations. A quadrupole interaction which varies dramatically with temperature is present, superposing with a magnetic interaction below the Néel temperature.     

MoCu3TeO7Cl2·0.5H2O

Single crystals of molybdenum(VI) tricopper(II) tellurium(IV) hepta­oxide dichloride hemihydrate, MoCu₃TeO₇Cl₂·0.5H₂O, were synthesized via a transport reaction in sealed evacuated silica tubes. All atoms occupy general positions within the triclinic () unit cell. The building units are irregular CuO₄Cl and CuO₃Cl₂ square pyramids, distorted TeO₃₊₁E trigonal bipyramids (E is the lone pair of Te^IV) and irregular MoO₅ pyramids. The TeO₃₊₁E, CuO₄Cl and CuO₃Cl₂ polyhedra form (110) layers bridged by Mo atoms. The water mol­ecules are located in [100] channels.     

NMR hyperfine spectrum of 143Nd in ferromagnetic cubic intermetallic NdAl2

The hyperfine spectrum of ¹⁴³Nd in NdAl₂ measured at T = 1.4 K provides values of ∣a_t∣ = 786 ± 0.5 MHz and ∣P_t∣ = 3.25 ± 0.03 MHz. The latter value is in agreement with the expected calculated value obtained from the 4f ground state wave function in a crystal field plus molecular field model, which may be deduced from inelastic neutron scattering experiments combined with susceptibility measurements, or from polarized neutron diffraction experiments. It is shown that the 4f electronic moment can be directly obtained from zero field NMR with good accuracy.     

Asymmetric decarboxylative Claisen rearrangement reactions of sulfoximine-substituted allylic tosylacetic esters

Allylic acetate esters containing a variety of N-arylsulfonyl sulfoximines on the acetyl residue have been prepared and submitted to the decarboxylative Claisen rearrangement reaction. Rearranged products were isolated in generally good yields, and diastereoselectivities up to 82:18 have been obtained. The N-(2,4,6-triisopropylphenylsulfonyl)-S-phenyl sulfoximine moiety gave the best selectivity. The stereochemistry of the major isomer was established by X-ray crystallography. A model to explain the stereochemical course of the rearrangement is proposed.     

Nova methodus adhibendi approximationem molecularium orbitalium ad plures iuxtapositas unitates

Résumé L'étude de la structure électronique d'une chaîne constituée par la répétition d'un motif polyatomique et l'interprétation des propriétés du polymère ainsi formé sont grandement facilités, s'il est possible de ramener les termes d'interaction entre unités voisines à un paramètre d'interaction unique. Ce problème a été traité en méthode des orbitales moléculaires par un procédé qui permet de tenir compte des modifications du monomère à l'intérieur du polymère et ne néglige que de faibles contributions.L'interaction entre deux monomèresi etj est représentée par la sous-matriceB _ij de dimensionn ×n formée par les termes non-diagonaux correspondants de la matrice-énergie. Par des transformations unitaires appropriées, il est possible de mettre sous forme diagonale les sousmatricesB _ij entre monomères voisins. En général, la diagonale de la matrice transformée contient un terme prépondérant qu'on peut considérer comme mesurant l'interaction (i, j). Une application numérique a été effectuée dans le cas d'un polymère fictif formé par des molécules H₂ et dans le cas d'un polymère peptidique formé par des groupements HNCO en interaction par l'intermédiaire de liaisons hydrogène. La validité des approximations introduites selon l'importance de l'interaction peut être vérifiée sur l'exemple d'un dimère dont les deux unités sont placées à des distances variables. Dans le cas d'un polymère les transformations effectuées conduisent à remplacer les orbitales atomiques du monomère par des orbitales s'étendant sur deux unités voisines; en prenant comme motif structural de la chaîne le monomère double formé par deux unités successives, on peut représenter l'interaction entre deux motifs adjacents par un seul terme.La réduction de la matriceB _ij à un seul terme fournit des bandes d'énergie dont la position est en très bon accord avec celles obtenues directement par les techniques classiques de calcul de l'état solide [7].

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The study of the electronic structure of a chain formed by repetition of polyatomic monomers and the interpretation of the resulting polymer are made much easier if the interaction terms relating to neighbouring units can be reduced to a single parameter. This problem has been treated in the MO scheme by a procedure which makes it possible to take into account the modifications of the monomer within the polymer and only neglects minor contributions.The interaction between two monomersi andj is represented by then ×n submatrixB _ij formed by the corresponding non diagonal terms of the energy matrix. By appropriate unitary transformations it is possible to bring the submatricesB _ij of neighbouring monomers to a diagonal form. In general, one of the diagonal elements thus obtained is much higher than the others, and can be taken as a measure of thei-j interaction. A numerical application has been made in the case of a fictitious polymer formed by H₂ molecules, and in the case of a polypeptide formed by HNCO groups interacting through hydrogen bonds. The validity of the approximations introduced for different values of interaction can be tested on a dimer whose units are placed at different distances. In the case of a polymer the transformations mentioned above require that the atomic orbitals of a monomer be replaced by orbitals extending over two neighbouring units. Taking as a new unit the corresponding pair of monomers, the interaction between the units can be represented by a single term. The reduction of theB _ij matrices to a single term each gives energy bands whose positions are in perfect agreement with those obtained directly by the classical techniques of solid-state physics [7].

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Zusammenfassung Das Studium der elektronischen Struktur von linearen Polymeren vereinfacht sich sehr, wenn die Wechselwirkung zwischen benachbarten Monomeren durcheinen Parameter beschrieben werden kann. Entsprechend wird im MO-Schema ein Verfahren entwickelt, das auf der Veränderung der Monomeren im Polymeren fußt.Die Wechselwirkung zwischen zwei Monomereni, j des Polymer wird durch eine aus Nichtdiagonalelementen der Hamiltonmatrix bestehende UntermatrixB _ij beschrieben. Für alle benachbarten Monomerenpaare lassen sich diese durch unitäre Transformationen diagonalisieren. I. a. ist eines der so erhaltenen Diagonalelemente vonB merklich größer und dient als Maß für die Wechselwirkung der beiden Monomeren. Angewendet wird die Methode auf ein fiktives Polymer aus H₂-Molekülen und auf ein Polymer aus durch H-Brücken verbundenen Peptidgruppen. Der Einfluß der Näherungen wird zunächst an einem Dinieren für verschiedene Abstände getestet.Im Falle eines Polymeren sind als Monomere Einheiten von zwei benachbarten Molekülen mit entsprechend ausgedehnten Orbitalen zu betrachten. Die Rechnung führt hier auf Energiebänder, deren Lage voll mit der nach klassischen Methoden der Festkörperphysik [7] erhaltenen übereinstimmt.

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Gratias agimus Cl. Vir.Raphaeli Del Re, qui nos, quod ad usum linguae latinae attinet, consilio benigne adiuvit.     

The spin density waves in chromium detected by hyperfine field measurements

The magnetic hyperfine field of tantalum nuclei in a high purity chromium matrix has been measured using the Time Differential Perturbed Angular Correlation technique. The spectra show that the hyperfine field is proportional to the amplitude of the spin density wave of chromium and that the tantalum probe nuclei do not clamp the phase of the spin density wave. The incommensurate antiferromagnetic first order phase transition as well as the spin flip transition have been observed. The temperature dependence of the hyperfine field is shown to deviate from the temperature dependence of the maximum magnetization of the spin density wave.     

Calcium imaging in the ant <Emphasis Type="Italic">Camponotus fellah</Emphasis> reveals a conserved odour-similarity space in insects and mammals

Background  

Olfactory systems create representations of the chemical world in the animal brain. Recordings of odour-evoked activity in the primary olfactory centres of vertebrates and insects have suggested similar rules for odour processing, in particular through spatial organization of chemical information in their functional units, the glomeruli. Similarity between odour representations can be extracted from across-glomerulus patterns in a wide range of species, from insects to vertebrates, but comparison of odour similarity in such diverse taxa has not been addressed. In the present study, we asked how 11 aliphatic odorants previously tested in honeybees and rats are represented in the antennal lobe of the ant Camponotus fellah, a social insect that relies on olfaction for food search and social communication.     

Comparison of perturbative and variational treatments of molecular vibrations: application to the vibrational spectrum of HFCO up to 8000 cm(-1)

We calculated highly excited states of the HFCO molecule, comparing results from two methods. In the first method, Van Vleck perturbation theory is used to transform away all off-diagonal couplings except those between nearly degenerate states. This perturbative transformation leads to a matrix representation where eigenvalues are obtained with relatively small matrices. In the second method, variational eigenvalues are obtained by combining the Jacobi-Wilson approach with the block-Davidson scheme. The key ingredient here is a prediagonalized-perturbative scheme applied to a subspace of a curvilinear normal-mode basis set. Comparisons of the two methods provide a critical test of the less time-consuming perturbation theory. Two different coordinate sets are used to test the sensitivity of the results to coordinate choice. Perturbation theory also requires a polynomial fit to the potential. The implications of this restriction are investigated.