Band 55, Heft 5

We have performed an investigation of the internal rotation of the methyl group in trans-cis ethyl vinyl ether by using molecular beam-Fourier transform Microwave (MB-FTMW) spectroscopy. Rotational spectra (up to J = 20) were recorded in the frequency region 4-19 GHz. Due to the internal rotation of the methyl group, some rotational transitions were split and the torsional barrier could be determined to V 3 (CH 3 ) = 1074.4(4) cm -1 .

The ground state rotational spectrum of H 2 C 18 O has been studied between 485 and 835 GHz with a sample of natural isotopic composition. Additional lines have been recorded around 130 GHz and near 1.85 THz, using a recently developed far-infrared laser-sideband spectrometer. The accurate new line frequencies were fit together with previously published data to obtain greatly improved spectroscopic constants. Both Watson's S and A reduced Hamiltonians have been employed yielding the rotational constants A A = 281 961.215 (82), B A = 36 902.275 51 (36), C A = 32 513.405 89 (36), A A = 281 961.371 (82), B A = 36 904.173 32 (91), and C A = 32 511.524 65 (86) MHz, respectively.

The ground state rotational spectrum of propyne has been studied in selected regions between 509 and 820 GHz spanning the quantum numbers 29

Fourfold coordination of trivalent metal ions by chlorines in molecular dimers changes from tetrahedral in Al 2 Cl 6 and Fe 2 Cl 6 to planar in Au 2 Cl 6 . Within an ionic model we interpret this transition in the stable molecular shape as due to the quadrupolar polarizability of the gold(III) ion. We also demonstrate within the same model that a mixed tetrahedral-planar coordination is stable in AUAlCl 6 and AuFeCl 6 clusters. Quantitative comparisons are presented for the calculated molecular structures and vibrational frequencies against the available experimental data from crystalline diffraction and from Raman spectra of the crystal and of vapours.

A series of europium doped Na 2 O-B 2 O 3 -SiO 2 , PbO-GeO 2 and ZnOTeO 2 glasses was investi-gated by means of 151 Mössbauer spectroscopy. The distortion of the Eu sites has been evaluated in the Na 2 O-B 2 O 3 -SiO 2 glasses by means of the quadrupolar interaction parameter and the asym-metry parameter; the disorder has been estimated by the line width. The occupancy of the sites in the borosilicate glasses is discussed. The correlation of the isomer shift with the optical basicity of the glass is discussed in terms of the degree of covalence of the Eu-O bond.

Lower and upper bounds as well as approximate formulas for the total π-electron energy (E) of benzenoid hydrocarbons are deduced, depending only on the number of carbon atoms (n) and number of carbon-carbon bonds (to). These are better than the several previously known (n, m)-type estimates and approximations for E.

The structure of clusters in methanol-water solutions in its dependence on the methanol mole fraction x M has been investigated by mass spectrometry on clusters isolated from submicron droplets by adiabatic expansion in vacuum and by X-ray diffraction on the bulk binary solutions. The mass spectra have shown that the average hydration number, (n m ), of m-mer methanol clusters decreases with increasing x M , accompanied by two inflection points at x M = ~0.3 and ~0.7. The X-ray diffraction data have revealed a similar change in the number of hydrogen bonds per water and/or methanol oxygen atom at ~2.8 Å. On the basis of both results, most likely models of clusters formed in the binary solutions are proposed: at 0 < x M < 0.3 the tetrahedral-like water cluster is the main species, at 0.3 < x M < 0.7 chain clusters of methanol molecules gradually evolve with increasing methanol content, and finally, at x M > 7 chain clusters of methanol become predominant. The present results are compared with clusters previously found in ethanol-water binary solutions and discussed in relation to anomalies of the heat of mixing of methanol-water binary solutions.

The structure of (C 2 H 5 NH 3 ) 3 Sb 2 Cl 9 • (C 2 H 5 NH 3 )SbCl 4 at 295 K has been determined. The crystals are orthorhombic, space group Pna2 1 (a -16.925(3), b = 24.703(5), c = 7.956(2) Å, V = 3326.4(12) Å 3 , Z = 4, d c = 2.018, d m = 2.01(1) Mg m -3 ). They consist of an anionic sublattice composed of two different polymeric zig-zag chains. One is built of Sb 2 Cl 9 3- units (corner sharing octahedra) and the other one is made of corner sharing SbCl 5 2- square pyramids. In the cavites between the polyanionic chains four non-equivalent ethylammonium cations are located. Three of them are disordered. The cations are connected to the anions by weak N-H...Cl hydrogen bonds. A first order phase transition of the order-disorder type was found at 274 K. It was studied by DSC, dielectric and X-ray diffraction methods. The mechanism of the phase transition is attributed to the ordering of at least one of the ethylammonium cations

Specific volumes of n-hexadecane (n-C 16 H 34 ) and n-heptadecane (n-C 17 H 36 ) are presented for temperatures between 298 and 348 K and pressures up to 280 MPa. The melting curve for n-C 16 H 34 was determined with differential thermal analysis. The pVT data are established for the liquid, solid and (in the case of n-C 17 H 36 ) rotator phases. For n-C 16 H 34 the density immediately below the freezing temperature is larger than for n-C 17 H 36 immediately below the rotational transition temperature. Changes of volume, enthalpy, and entropy along the phase transitions are reported. The volume change of melting decreases distinctly with increasing pressure, whereas the volume change at the rotational transition is much less pressure-dependent. Enthalpy and entropy changes have been calculated with the aid of the Clausius-Clapeyron equation

The formulas of the g-factors g II , g ┴ and the hyperfine structure constants A II .A ┴ for 3d 7 ions in tetragonal octahedral crystals are established from a cluster approach. Differing from previous formulas, in these formulas the role of configuration interaction (CI)-and covalency (CO)-effects is considered, and the parameters related to both effects are obtained from the optical spectra and the structural parameters of the studied crystal. From these formulas, the EPR parameters g i and A i for K 2 ZnF 4 :Co 2+ are calculated. The results show good agreement with the observed values. The contributions to the EPR parameters g i and A i , from the CI and CO effects, and the relationship between the sign of Δg(=g ┴ - g II ) and the tetragonal distortion (elongated or compressed) of the ligand octahedron are discussed

Painleve analysis is used to study the complete integrability of the recently proposed Konno-Onno equation, which also leads to a general form of solutions of the system. An independent study, using the prolongation theory, gives the explicit form of the Lax pair which is then used to obtain the Backlund transformation connecting two sets of solutions of the system. The existence of the Lax pair and the positive result of the Painleve test indicate the complete integrability of the system

Using the thermochromic shift method of absorption and fluorescence spectra, the dipole moments in the ground, µ g , and excited. µ e , state are simultaneously determined for PRODAN in ethyl acetate. The obtained values for µ g and µ e are compared with those previously determined by the solvatochromic method for two different Onsager radii, and a satisfactory agreement has been obtained

The results of comparison of experimental 35 C1 NQR parameters for a great number of organic and organometallic compounds and estimated ones using ab initio calculations at the RHF/6-31G(d) level were systematized. The NQR frequency changes on going from one compound to another depend, in general, on the changes of populations of the CI atom p o -orbitals in these compounds and, first of all, of populations of their less diffuse parts

Mean amplitudes of vibration of the recently described square-bipyramidal [ReFBr 5 ] 2- anion have been calculated from vibrational spectroscopic data, over a wide temperature range. The results are briefly discussed in relation with its structural peculiarities and some comparisons with related species are made