Linear and non-linear response of embedded Na clusters

We investigate Na clusters embedded in Ar matrices. The surrounding Ar atoms are modeled in terms of their dynamical polarizability and the strong electron repulsion. The calibration of the model is discussed. First results for the non-linear optical response of the Na clusters are presented for the test case of Na₈ embedded in Ar ensembles of different sizes. It is shown that blue shift through core repulsion and red shift through dipole polarizability counterweight each other to the end that very little global shift is seen in the spectra. This feature persists to all excitation strengths considered. There are, however, detailed effects, such as for example the Landau fragmentation of the Mie plasmon peak. PACS 36.40.Gk; 36.40.Vz; 31.15.Ew     

On two-dimensional supergravity and the quantum super-Möbius group

We describe the quantum-group structure of two-dimensionalN=1 supergravity in the conformal gauge. The operator-algebra of this (super-Liouville) theory is shown to correspond to a quantum deformation of the super-Möbius group, which provides a new solution of Yang and Baxter's equation. This structure is used to investigate the strong-coupling regime of the theory (1d9). Ford=5, a unitary truncation theorem-similar to the one of the bosonic case-is derived for the fundamental representation.Unité Propre du Centre National de la Recherche Scientifique, associée à l'École Normale Supérieure et à l'Université de Paris-Sud     

Presentation and central extensions of mapping class groups

We give a presentation of the mapping class group of a (possibly bounded) surface, considering either all twists or just non-separating twists as generators. We also study certain central extensions of . One of them plays a key role in studying TQFT functors, namely the mapping class group of a -structure surface. We give a presentation of this extension.

     

Vibronic contributions to the n → π* absorption band of cyclopentanone. An ab initio SCF-RPA calculation

The SCF-RPA scheme is applied to the n → π* absorption band of cyclopentanone in its (C₂) ground-state nuclear configuration. Using the Cederbaum—Domcke algorithm, the effects of the (ν₃) C=O stretching, (ν₁₈) ring puckering and (ν₂₅) C=O out- of-plane vibrations are investigated. The calculated spectrum shows both allowed and vibronic components, in agreement with the experimental observations of Howard-Lock and King.     

PHOTOCHEMISTRY OF SOME FURO (3,2-g)-COUMARIN AND 2,3-DIHYDROFURO (3,2-g)-COUMARIN DERIVATIVES

Abstract— In order to gain further insight into the photocrosslinking of DNA by furocoumarin derivatives, the photoreactivity of furocoumarins and bisfurocoumarins was studied. While the triplet dimerization of furocoumarins occurs at the pyrone side, incorporation of furocoumarins in nonconjugated bichromophoric systems leads to reactions at the furan side as well. Furthermore, 2,3-dihydrofurocoumarins show both triplet and singlet reactivity.     

Farinfrared absorption in Al2O3 and MgO

Far-infrared absorption measurements performed in Al₂O₃ and MgO between 300 and 1 500 K with a Fourier scanning interferometer are reported. A temperature analysis of results based on a phonon self-energy model allows to assign the absorption in this region to 2- and 3-phonon difference processes. The contributions of these processes are separated and discussed. In Al₂O₃, the frequency dependence of the absorption is also analyzed. A good overall agreement between theory and experiment is evidenced.     

Crystal and Molecular Structure of the 4:3 Complex between Lanthanum Nitrate and Pentaethyleneglycol Dimethyl Ether

The crystal and molecular structure of [La(NO₃)₃]₄(C₁₂H₂₆O₅)₃ has been determined from low-temperature single-crystal X-ray diffraction data. The complex crystallizes in the monoclinic space group I2 with Z = 2. Lattice parameters at 150 K are a = 12.234 (6) Å, b = 11.105 (5), c = 26.613 (9), β = 90.65 (4)°. The structure was solved by Patterson and Fourier techniques and refined to a conventional R_F-value of 0.068. The compound contains three dinitrato complex cations [La(NO₃)₂C₁₂H₂₆O₆]⁺ with 10-coordinate lanthanum ions and one hexanitrato anion, [La(NO₃)₆]^3?, with a 12-coordinate La(III)-ion. One complex cation has a C₂-symmetry while the two others, which are crystallographically equivalent, have no symmetry and contain a disordered ligand molecule. The polyther adopts a ring-like conformation in all the complex moietis. The La? O(nitrate) distances lie in the ranges 2.52–2.53 and 2.49–2.62 Å, with average values of 2.53 (7) and 2.56 (6) Å, respectively, fo the species with C₂- and C₁-symmetry; the La? O(ether) bond lengths lie int he range 2.54–2.79 Å (average: 2.6 (1)) for the C₂-moiety and their mean value amounts to 2.6 (2) for the disordered species. The hexanitrate has a C₂-symmetry and the La? O distances range between 2.56 and 2.67 Å with an average value fo 2.64 (4) Å. The effective ionic radii of the 10- and 12-coordinate La(III) ions are estimated as 1.28 and 1.33 Å, respectively.     

The α2‐polymorph of salicylidene­aniline

N‐Salicylideneaniline (SA), C₁₃H₁₁NO, belongs to the large family of aromatic Schiff bases. It is of particular importance owing to its reversible photoreactivity. SA forms two photochromic polymorphs, both with two non‐coplanar benzene rings. In addition, we have recently discovered a planar polymorph, named the β‐polymorph, which will be discussed in a subsequent paper. We report here the structure of the α₂‐polymorph in the orthorhombic crystal system. This compound exhibits a strong intra­molecular O—H⋯N hydrogen bond and the dihedral angle between the two rings varies with temperature.