Band 46, Heft 3

The present 2 H NMR study gives some evidence that a film of fluorobenzene of about one monolayer thickness on graphite undergoes a 2D phase transition from a fluid like into a rotationally disordered solid phase at ca. 160-130 K, and subsequently a 2D solid-solid transition into an ordered phase at a temperature about 90 K. A multilayer film (Θ= 8) decomposes below about 200 K into a 3 D bulk solid phase and an adsorbed film, of presumably monolayer thickness. It is concluded that the monolayer film spreads uniformly on the available surface with flat orientation of the molecules. These detailed statements can be obtained because the combined action of the intramolecular quadrupole interaction and the extramolecular magnetic shielding type coupling allows to relate the Z-axes of coordinate frames fixed in the support and fixed in the adsorbed molecule.

The structure and properties of a 1.791 molal aqueous LiF solution is investigated by performing molecular dynamics simulations using a water model with both bond flexibility and instantaneously responsive polarization. On average, each cation is in close contact with about one anion. This causes a strong overlap of the hydration shells and an almost complete breakdown of the surrounding water structure. While the lone pairs of the hydration waters in the first Li + shell occupy preferentially tetrahedral positions, the orientational distribution of the solvent molecules around F -- is quite uniform. By comparing various autocorrelation functions of water molecules in the solution and in the pure liquid, the influence of solvated ions on the translational, rotational and vibrational motions of hydration water can be studied

We recorded the microwave spectrum of hexafluoropropanone between 7 and 15 GHz using a pulsed molecular beam microwave Fourier transform spectrometer. The rotational constants were determined to be A = 2181.71980(14) MHz, B= 1037.22930(7) MHz, C = 934.89233(8) MHz, the quartic centrifugal distortion constants are D' J = 0.07378 (39) kHz, D' JK = 0.10002(75) kHz, D' K = -0.07269(266) kHz, δ' J = 0.00623(29) kHz and R' 6 = 0.00755(12) kHz. Stark effect measurements yielded a dipole moment μ = μ b = 0.3949 (18) D

The influence of the calculation procedure on the energy characteristics of vacancies and helium impurities in α-iron is considered. Calculations are performed with the help of long-range oscillating interatomic pair potentials found on the basis of a model pseudopotential approach. It is shown that for improving the convergence of the lattice sums one must introduce space windows. The best results were obtained with the Vashista-Singwi local-field correction and the modified windowmodulation interatomic potential based on the Heine-Abarenkov pseudopotential with the Animalu formfactors

The temperature dependence of 35 C1, 81 Br, and 127 I NQR frequencies and 1 Hspin-lattice relaxation times (T 1 ) for CH 3 NH 3 PbX 3 (X = Cl, Br, I) was measured through the successive phase transitions in these solids. The isotropic reorientation of the CH 3 NH 3 ions takes place in the higher-temperature phases (tetragonal [I4/mcm] and cubic) of the three salts (E a = 11 kJ mol -1 ). T 1 's in the lowest-temperature phases (orthorhombic) indicate that the cations undergo correlated C 3 -reorientation in the chloride (E a = 5.45 kJ mol -1 )and in the iodide (E a = 5.80 kJ mol -1 , whereas correlated (E a = 2.40 kJ mol -1 ) and uncorrected (E a = 7.50 kJ mol -1 ) C 3 - reorientations are excited in the bromide. It is also revealed that the rotational tunneling of the cations governs T 1 at lowtemperature region in the orthorhombic phases of these salts

MINDO-Forces calculations have been performed, with complete optimization of geometry on fulvene and X-fulvene radical anions, where X is OH, NH 2 , CH 3 , NO, 2 CN, F, dimethyl and cyclopropyl. A twisted structure with angle 5° was found for fulvene anion. All substituents are stabilizing. The stabilization effect is more pronounced in the case of NO 2 , and very weak in the case of CH 3. It was found that the substituents CH 3 and CN show amphielectronic behaviour. Geometrical parameters, heats of formation, dipole moments, electron and spin densities are reported

There is a general belief that under small velocity approximation. Special Relativity goes over into Galilean Relativity. Should this be interpreted exclusively in terms of the kinematical symmetry transformations (Lorentz vs. Galilei) a misconception could easily arise that would stem from overlooking the role of conventionality ingredients of Special Relativity Theory. It is observed that the small velocity approximation cannot alter the convention of distant simultaneity. In order to exemplify this point further, the Lorentz transformations are critically compared, under the same approximation, with two other space time transformations, one of which represents an Einstein world with Galilean synchrony whereas the other describes a Galilean world with Einsteinian synchrony

In the photoreactions of polycyclic aromatic hydrocarbons with tetrachloromethane in binary mixtures of tetrachloromethane with cyclohexane, benzene and acetonitrile, both the quenching of the fluorescence and the photoreactions run through an intermediate stage which is an exciplex of the excited hydrocarbon with tetrachloromethane. Abnormal quantum yields of the hydrocarbon decrease are interpreted in terms of the appearance of a new reaction channel via a triplex consisting of the excited hydrocarbon, solvent and tetrachloromethane. The photoreaction is quenched by diphenylpicrylhydrazyl, thus suggesting the radical nature of the chemical transformations. A kinetic scheme is suggested for the photophysical and photochemical processes describing the observed phenomena.

The 1 H spin-lattice relaxation time (T 1 ) in solid (CD 3 ) 3 CNH 3 Cl and (CD 3 ) 3 CNH 3 Br was measured above room temperature and the motional parameters for the reorientation of the NH 3 + groups were determined. The 1 H NMR absorptions measured in the same temperature range for (CH 3 ) 3 CNH 3 Cl and (CH 3 ) 3 CNH 3 Br indicate the presence of superimposed several cationic motions commonly taking place in both compounds. From X-ray powder patterns taken at room temperature, the bromide was found to be isomorphous with the chloride

The frequency response of the polarized emission of Y t -base in n-propanol at -20°C was measured. Excitation wavelengths of 346, 312 and 285 nm were used for which the fundamental anisotropics were 0.32, 0.19 and 0.04, respectively. Additional data were obtained using CCl 4 to decrease the mean decay time from 10 ns to 0.7 ns. These nine sets of data were analyzed globally to recover the anisotropy decay law. Two correlation times, of about 146 ps and 502 ps, were needed for a good fit

Quantum chemical calculations of relative energies and vibrational frequencies have been performed in order to elucidate the structure of metalated aminonitriles ( 1 R 2 RN) 3 RC 2 NLi formed upon lithiation of ( 1 R 2 RN) 3 RCH-CN in tetrahydrofuran at -78 °C. For the sake of feasibility the calculations have been performed on model compounds where the heavy substituents 1 R, 2 R and 3 R and in some cases even the complete amino group ( 1 R 2 RN) and 3 R have been replaced by hydrogen atoms. In the gasphase a lithium-bridged (nonclassical) monomer, whose lithium atom is within bonding distance to the atoms of the cyano group and the adjacent carbon atom, was found to be about 9 kcal/mol lower in energy than the most stable isomer of the corresponding nitrogen metalated ketenimine with amost linear CNLi moiety. However, the relative stability of the two structures will most likely be reversed under the influence of a solvent (modeled by H 2 0). Dimerization of H 2 C 2 NLi, yielding a product of D 2h symmetry with a four-membered (LiN) 2 ring, turned out to be exothermic by about 41 kcal/mol in the gasphase and 15 kcal/mol when the model solvent is present. While in the case of the lithiated amino ketenimine with almost linear CNLi segment the structure obtained with the semiempirical MNDO method widely parallels the ab initio results, the semiempirical method seems to perform less reliably for the nonclassical monomer. Formation of the trapping products obtained with methyl iodide and acetyl chloride is explained in terms of orbital- and charge control, respectively. According to this analysis, the results of trapping experiments are compatible with presence of a dimer, of a monomer with almost linear CNLi moiety, or of a monomer with lithium in a bridging position. However, comparison of observed and computed vibrational frequencies and of the calculated energies of classical and nonclassical structures led to the conclusion that the observed IR spectra are not due to nonclassical molecules with lithium in a bridging position. Taking into account the results of recent cryoscopic measurements we assign the characteristic absorptions in the experimental IR spectra to keteniminelike monomers and their dimers

The effects of dipolar coupling between a deuteron and a spin-½ nucleus on the deuterium quadrupolar echo is calculated. Due to the dipolar coupling the quadrupolar echo amplitude is shown to decay to 1/2 times its initial value for t →∞

Perhydrocoronene has recently been studied as a matrix in low and high temperature luminescence spectroscopy of aromatic compounds. Perhydrocoronene has been found to be a by-product formed during the catalytic hydrocracking of a petroleum feedstock. The isolation and purification of spectroscopy grade perhydrocoronene is described in detail