Band 53, Heft 1-2

The present contribution reports on the analysis of the high resolution FTIR spectra of the only two IR-active parallel fundamentals ν 11 and ν 12 of the isotopomers 12 C 3 14 N 3 H 3 , 13 C 3 14 N 3 H 3 , 12 C 3 15 N 3 H 3 , C 3 15 N 3 H 3 and 12 C 3 14 N 3 D 3 , respectively, of 1,3,5-triazine. The molecular constants of the ground state and the upper states ν 11 = 1 and ν 12 = 1, respectively, for all molecules under consideration are listed. The enhancement of the P-and the depletion of the R-banches, observed in the v 11 bands of all non-deuterated isotopomers, is discussed, and the Herman-Wallis constants obtained are given.

We theoretically investigate the Güémez-Matias method for controlling chaotic behaviour. We obtain an algorithm to determine the value of the control parameter γ. Numerical simulations confirme our theoretical approach.

Molecular dynamics simulation of molten NaCl was carried out at 1200 K with well defined potential parameters. The chemical potential of the melt was satisfactorily estimated with the method pro-posed by Powles et al., which requires only positional data of the ions at the temperature in question, when the number of ions in the basic cell is large enough.

A linear stability analysis of a novel electrohydrodynamic Kelvin-Helmholtz system consisting of the superposition of two uniformly rotating dielectric media is presented. The characteristic equation for such an arrangement is derived, which in turn yields a stability criterion for velocity differences of disturbances at a given rotation frequency. The conditions of stability for long and short wave perturbations are obtained, and their dependence on rotation, surface tension and applied electric field is discussed. Limiting cases for vanishing fluid velocities, rotation frequency, and applied electric field are also discussed. Under suitable limits, results of previous works are recovered. A detailed analysis for tangential and normal applied electric fields, in the presence and absence of surface charges, is carried out.

57 Fe Mössbauer spectra have been measured at various temperatures between 4.2 K and 300 K for iron langbeinites A 2 Fe 2^04)3 with A = K, NH 4 , Rb, T1 and magnesium, manganese and cadmium lang-beinites doped with Fe" + . The spectra revealed several contributions whose isomer shifts and quadru-pole splittings have been obtained by fitting program routines. For the high-temperature cubic phases two crystallographically non-equivalent iron sites have been identified, characteristic of Fe 2+ in the high-spin state. Abrupt changes of the quadrupole couplings indicated phase transitions; in some cases, the spectra have also revealed several sites for Fe 2+ in low temperature phases. From the temperature dependences, phase transition temperatures, crystal field splittings and Debye temperatures have been derived.

The electronic properties of the C 6 H 6 and C 6 D 6 molecules have been studied by an all-quantum approach, where the classical and quantum degrees of freedom of the nuclei are taken into ac-count in the evaluation of electronic expectation values. In the all-quantum approach suggested a Feynman path integral Monte Carlo (PIMC) formalism has been linked to an electronic ab initio Hamiltonian. The electronic expectation values have been calculated as averages over the manifold of nuclear configurations populated in thermal equilibrium. This theoretical setup leads to electronic expectation values that depend on the temperature and on the mass of the nuclei. The ensemble averaged electronic properties differ sizeably from the results derived on the basis of a single nuclear configuration of minimum energy. This behaviour should have physical implications for the theoretical calculation of electronic momentum properties such as Compton profiles, reciprocal form factors, etc. We describe an error source in the theoretical determination of electronic momentum properties which has not been commented so far.

Internal cation mobility ratios in the molten system KCl-DyCl 3 have been measured at 1093 K by Klemm's countercurrent electromigration method. From these, and data available on the conductivities and molar volumes of the mixtures, the internal mobilities b of both cations have been calculated. With increasing concentration of Dy, b K decreases. The decrease of b K is attributed to the tranquilization effect by Dy 3+ ions which strongly interact with Cl - ions. With increasing concentration of K + , b Dy decreases; this may be attributed to the stronger association of Dy 3+ with C - ions due to the enhanced charge asymmetry of the two cations neighboring to the C - ions. It could not been clarified whether a species such as [DyCl 6 ] 3- is also an electrically-conducting species in the K + rich range.

A deterministic entropic measure is derived for the time evolution of Newtonian N-particle systems based on the volume of the instantaneously occupied phase space (IOPS). This measure is found as a natural extension of Boltzmann's entropy. The instantaneous arrangement of the particles is exploited in the form of spatial correlations. The new entropy is a bridge between the time-dependent Boltzmann entropy, formulated on the basis of densities in the one-particle phase space, and the static Gibbs entropy which uses densities in the full phase space. We apply the new concept in a molecular dynamics simulation (MDS) using an exactly time reversible “discrete Newtonian equation of motion” recently derived from the fundamental principle of least action in discretized space-time. The simulation therefore is consistent with micro-time-reversibility. Entropy becomes an exact momentary observable in both time directions in fulfillment of a dream of Boltzmann.

In the solid state, the conformation of N-actetylprolinamide is stabilized by two intermolecular O···H bridges and one intramolecular N···H hydrogen bond. According to quantum chemical ab initio calculations with the 6-31+G* basis set at the one-determinant level, the intramolecular N ···H bond is not strong enough to maintain the solid-state molecular conformation the gas phase. The conformational changes predominantly consist in a rotation of the amide group about its C-C bond to the proline ring, resulting in a c/s-like conformation which is stabilized by a presumably stronger intramolecular O···H bond between one hydrogen atom of the NH 2 group and the carbonyl oxygen of the acetyl subsituent bonded to the nitrogen atom of the five-membered ring. These confirmational changes cause a reduction of the molecular dipole moment by about 50%, indicating that the conformation in solution might be strongly solvent dependent. While both the MINDO/3 and the MNDO method in their standard parametrizations fail to reproduce the ab initio results, the lattice effect is reproduced at least qualitatively with the PM3 as well as with the AM1 method.

The molecular Zeeman effect is reported for norbornadiene at fields near 18 kG. The experimental results are for the molecular g-values: g aa = 0.02860(16), g bb = 0.05271(11), g cc = 0.00142(26), for the magnetizability anisotropics: 2ξ aa - ξ bb - ξ cc = -0.41(26) · 10 -6 ergG -2 mol -1 , 2ξ bb - ξ cc - ξ aa = +40.72(27) · 10 -6 erg G -2 mol -1 and for the molecular electric quadrupole moments: Q aa = -1.78(20) · 10 -26 esu cm 2 , Q bb = 3.73(20) · 10 -26 esu cm 2 , Q cc = -1.94(30) · 10 -26 esu cm 2 , with the c-axis of the molecular inertia tensor aligned to the C 2v -axis of the equilibrium configuration. The results of ab-initio calculations, using London type atomic orbitals as basis functions, are reported for the g-tensor, the magnetizability tensor and the molecular electric quadrupole moment tensor and are compared to the experimental findings. The possibilities of strain induced magnetizability exaltations and of systematic differences between gas phase and bulk phase magnetizabilities are discussed.

13 C NMR spectroscopic measurements of aqueous solutions containing alkaline earth metal chloride and a carboxylic acid have been carried out to acquire some insight into the coordination manners of various carboxylic acids to alkaline earth metal ions. The dependence of the 13 C NMR signal positions of the carboxylate carbons on the magnesium ion concentration in a magnesium carboxylate system is a good index to understand the coordination manner of the carboxylate ion. The upfield shift of the carboxylate carbon signal with increasing magnesium ion concentration indicates that the carboxylate ion acts as a bidentate ligand to form a ring structure. Only in the citrate systems, the existence of a relatively stable complex is evidenced in which the citrate ion is expected to act as a tridentate ligand.