Volume 45, Issue 8

The quantum statistical frame for infinite multi-lattice spin systems is introduced. The thermodynamic functionals specific internal energy, entropy and free energy are shown to exist on the set of permutation invariant states for polynomial mean field interactions by direct estimation methods. Their dependence on the relative sizes of the sublattice systems is made explicit. The set of homogeneous minimal free energy states is shown to be a Bauer simplex which contains all limiting Gibbs states. For the extremal minimal free energy states the self-consistency equations are derived.

A vibration-rotation band system of acetylene of the /Π u bending vibration v 5 has been recorded with high resolution by a Bruker IFS 120 HR Michelson spectrometer. From the analysis of the hot band of the normal isotopic species, v 4 + v 5 - v 4 , and the fundamental band of HC 13 CH in natural abundance an improved set of constants has been derived. The intensity perturbation due to the l-type resonance has been clearly observed in the band system v 4 + v 5 -v 4

The formal analogy between the distribution of the electromagnetic field in waveguides and microwave cavities and quantum mechanical probability distributions is put into evidence. A waveguide of a cut-off frequency ω c acts on an electromagnetic wave as a quantum potential barrier U g = hω c . A non-habitual time independent Schrödinger equation, describing guided wave propagation, is established

An experimental model of a Duffing oscillator is presented. It consists of a linear inductance, a resistance and a ferroelectric nonlinear capacitance. A computer controlled measuring system recorded quantitatively the phase portrait of this series-resonance circuit. The comparison of experimentally observed phase portraits with those calculated by a computer allows to check different assumptions about the nature of the nonlinear properties

Classical hamiltonian perturbation theory formulated in terms of action-angle variables is applied to develop a general and systematic method for calculating the influence of anharmonic perturbations on the motion of a charged particle in a Penning trap. Action-angle variables are ideally suited to determine the shifts of the characteristic frequencies in a perturbed orbit. The application of the method is demonstrated by several case studies

Assuming a sufficiently low density of the trapped particles the methods of equilibrium statistical mechanics for non-interacting particles are used to find expectation values and distribution functions for the most interesting 1-particle observables. The results are applied in a perturbation calculation to estimate space charge effects at low particle densities

The rotational spectrum of l-isocyanoprop-2-yne, HC≡CCH 2 NC, has been measured in the vibrational ground state by microwave Fourier transform spectroscopy from 5 to 26.5 GHz. The nuclear quadrupole hyperfine splittings due to 14 N have been analysed to obtain the coupling constants χ aa = 290.3(78) kHz, χ bb = 10.6(80) kHz and χ cc = -300.9(80) kHz

The methyl torsional fine structure in the rotational spectrum of gauche butane in the vibrational ground state was investigated in the frequency range between 10 and 141 GHz. Using the internal axis method (IAM) in the formulation of Woods, all internal rotation parameters were determined with high accuracy. The barrier height of the methyl internal rotation was determined to 11.34 (29) kJ/mol (2.710 (69) kcal/mol)

The dielectric relaxation of water rich aqueous solutions of ethanol, ehtylene glycol, glycerol, diethylene glycol, 1,2-butanediol, 1,3-butanediol and 1,4-butanediol has been measured at 20 °C. In all cases the fitting of the data by a sum of Debye type spectral components allows for two description modes which can be interpreted as a collective alteration of the water relaxation or, on the other hand, as formation of a microheterogenous solution where "affected" and "unaffected" water becomes discernible

The influence of solvent on the UV-visible absorption and luminescence spectra of some highly fluorescent vitamin B 1 derivatives, the products of the reaction of N-methylated vitamin B 1 with cytidine (I), adenosine (II) and 2-amino-4-methylpyridine (III) is studied. Spectroscopic manifestations of protonation of I and II are also investigated using a semiempirical INDO/S CI method. Singlet and triplet energy levels of the free ion and several protonated species are calculated, and transition energies and oscillator strengths are compared with the experimental spectra. Calculated charge densities on heteroatoms in the ground and excited singlet and triplet states are correlated with changes of the experimental pK a values with excitation. The results for I and II are compared with those for the trimethylated pyrichrominium ion (III) previously studied

The conductance of HCl and HBr in water-dimethylformamide (DMF) mixtures of 10-80 wt % DMF at 25 ºC has been measured and discussed, using the three parameter conductance equation suggested by Fuoss et al. in 1965. The ionic conductances and Waiden products of the H + , C - and Br - ions have been determined and explained. No appreciable ion-association of these acids in these media has been found

Monte Carlo simulations of muscarine water solution were carried out using ab-initio SCFLCAO- MO interaction potentials. The overall results indicate that in water solution the preferred conformation, on the basis of enthalpic considerations, should be the one having the dihedral angle H02-02-C4-H4, τ, equal to 180°. The molecule shows a first hydration shell with about 35 water molecules: of these only about 25 are constantly present, 18 are at a distance equal to lower than 2.5 A and only 5 have an interaction energy larger than -21 kJ/mole. The results do not support the hypothesis that the role of Ol in muscarinic activity is that of increasing hydrophylic bonds

The lattice vibrations of the ß-rhombohedral boron structure group are investigated in detail by group theory. IR spectra of pure ß-rhombohedral boron as well as of B: Mn, B: Fe, B: Cu, and B: Cu/Al are presented and discussed. In comparison with boron carbide most of the absorption bands can be associated with certain vibrations. The vibration frequencies are determined by application of the phenomenological theory of Waser and Pauling, which thus yields a reliable estimation of the restoring forces ion these solides

The temperature dependence of the chlorine NQR spin-lattice relaxation time T 1Q was observed for trimethylsulfonium hexachlorometallates(IV), [(CH 3 ) 3 S] 2 MCl 6 (M = Pt, Sn), trimethylammonium hexachlorostannate(IV), [(CH 3 ) 3 NH] 2 SnCl 6 , and tetramethylphosphonium hexachlorostannate(IV), [(CH 3 ) 4 P] 2 SnCl 6 . The quadrupolar relaxation in [(CH 3 ) 3 NH] 2 SnCl 6 and [(CH 3 ) 4 P] 2 SnCl 6 can be described by the usual librational and reorientational motion of the complex anion at lower and higher temperatures, respectively. Besides T 1Q due to these two mechanisms, T 1Q minimum was observed at ca. 90 and 120 K for [(CH 3 ) 3 S] 2 PtCl 6 and [(CH 3 ) 3 S] 2 SnCl 6 , respectively, which is attributable to the electric field gradient modulation by the motion of the [(CH 3 ) 3 S] + cation having lone-pair electrons. The activation energies for the isotropic reorientation of the complex anion were determined as 46, 65, 59, and 60 kJ mol -1 for [(CH 3 ) 4 P] 2 SnCl 6 , [(CH 3 ) 2 NH] 2 SnCl 6 , [(CH 3 ) 3 S] 2 PtCl 6 , and [(CH 3 ) 3 S] 2 SnCl 6 , respectively

After a discussion of the one-component Schrödinger (1926) and the four-component Dirac (1928) representation of hydrogen it is shown that the six-component electrodynamic picture is considerably simpler and clearer. The computational effort is reduced to a fraction

Some general aspects of the concept of molecular topology are delt with. The role of the separability of topological and non-topological factors that determine molecular properties, as well as the "holistic" behaviour of certain classes of compounds are discussed. A suggestion regarding a deeper understanding of the role of molecular topology is made

We report on first experiences with a pulsed molecular beam microwave Fourier transform spectrometer with parallel molecular beam and resonator axes. This setup shows up a high resolution and sensitivity.

The temperature and enthalpy of melting have been studied in the range up to 0.55 GPa by means of differential scanning calorimetry. In the range below a triple point at (498 ± 5) K and (0.27 ±0.02) GPa the results can be expressed by means of linear relations: 7 = 476 + 80 p, and AH = 22.4- 29.8 p, where the corresponding units are K, kJ/mol and GPa. Above the triple point the correlation between pressure and temperature corresponds to Simon's equation, p = 0.27 +1.57 x 10 -3 (T-498) 1.28 , and the enthalpy of melting decreases linearly with the pressure: ΔH = 9.50-10.65 (p-0.28). Comparison is made with a recent study by Sinitsyn et al

In the study of semiconductor electronic breakdown we observe the self-generated formation of spatio-temporal dissipative structures, when a bias voltage is applied at liquid-helium temperature. The underlying nonlinear physics of impurity impact ionization reveals critical phase transition behavior by varying the temperature at constant voltage