Band 46, Heft 4

Based on the linear coupling term in the non-relativistic quantum theory of matter-photon interactions, the coupling of a finite dimensional quantum system (finitely many finite-level atoms) with the boson gas (radiation field) in thermal equilibrium by means of perturbation theoretical methods is calculated. For the perturbation term of the Dyson expansion the unbounded interaction operator is taken. By a detailed analysis of the perturbation integrals and series, it is possible to derive the trace-class property of e -ßH , where H is the corresponding hamiltonian of the interacting systems and ß the inverse temperature

The effect of 2-substitutions (NH 2 . O, CH 3 O, CI. Br) in 3-methylquinoxalines on the fluorescence and phosphorescence band position and intensity at 293 K, and the temperature dependence of their fluorescence and phosphorescence quantum yields were investigated in polyvinyl alcohol) films

X-ray scattering measurements have been done on aqueous MgCl 2 -KCl and MgCl 2 CsCl solutions saturated with their double salts of MgCl 2 • KCl • 6 H 2 O and MgCl 2 • KCl • 6 H 2 O respectively, at 293 K. The Mg 2+ ion was found to be coordinated with six water molecules at an Mg-O distance of 209 and 208 pm, respectively, whereas K + and Cs + ions were surrounded by both water molecules and chloride ions in the first coordination sphere. The interatomic distance between the alkali cation and the chloride ion was 320 pm and 339 pm for K + and Cs + , respectively, and the coordination numbers of K + and Cs + with respect to CP were 2.4 and 2.0, respectively. The alkali metal H20 distance and the hydration number of the cation were 277 pm and 3.7, respectively, for K + and 315 pm and 4.7, respectively, for Cs + . The structures of the solutions are discussed in connection with the nucleation processes of the salts from the aqueous solutions

A circular scale of time is proposed and applied to the calculation of the Rayleigh-Schrödinger perturbation energy for a non-degenerate state

The Rietveld profile refinement has been applied to X-ray powder diffraction data on Naß''-gallate, a solid electrolyte isostructural with Naß''-alumina and characterized by different types of lattice defect. Several structural models have been refined and discussed in order to understand if a statistical comparison of the structure discrepancy factors can be used as a reliable criterion to retain or reject structural changes from one model to the other. It is shown that, due to the correlation between structural parameters and to the poor sensitivity of the structure discrepancy factors to chemical composition, some care is necessary to direct correctly the refinement and to obtain a reliable structural model

The phase transitions in CsSnCl 3 and CsPbBr 3 have been studied by X-ray powder diffraction, by 81 Br-NQR and by 'H-, 119 Sn-, and 113 Cs-NMR. At room temperature in air CsSnCl 3 forms a hydrate which can be dehydrated to the monoclinic phase II of CsSnCl 3 . The high temperature phase I has the Perovskite structure, as the X-ray and NMR experiments show. The three phases of CsPbBr 3 , known from literature, have been corroborated. The results are discussed in the framework of the group ABX 3 , A = alkalimetal ion, B = IV main group ion, and X = Halogen ion

The molecular motion in (CH 3 ) 3 XCl, X = Sn and Pb has been investigated by measurement of the second moment M 2 ( 1 H) as function of temperature in the range 95 < T,/K<345. The methyl groups in both compounds rotate freely over the whole temperature range studied. In (CH 3 ) 3 SnCl the C' 3 -rotation of (CH 3 ) 3 Sn-group about the Sn CI axis sets in above 273 K. To explain the NMR and INS results, the crystal structures of (CH 3 ) 3 PbCl and CH 3 SnBr 3 were determined by single X-ray diffraction. (CH 3 ) 3 PbCl crystallizes in a monoclinic space group C 3 2 -C2, a = 1276.7(3) pm, b = 982.3(3) pm, c = 547.0(2) pm, ß = 91.12(1)°; Z = 4, R = 0.035. CH 3 SnBr 3 crystallizes in an orthorhombic space group D 16 2h -Pnma, a = 643.0(3) pm, b= 1005.3(4) pm, c= 1148.0(4) pm; Z = 4, R =0.057

Pyrophthalone (PP, 2-(2-pyridinyl)-l H-indene-l,3(2H)-dione) and quinophthalone (QP, 2-(2-quinolinyl)- l H-indene-1,3(2 H)-dione) were investigated in various solvents with respect to their photostability. It was found that PP and QP in ethanol as well as QP in cyclohexane are rather stable under steady-state conditions using UV light (λ = 253.7 nm). Conventional as well as laser flash photolysis of airfree aqueous alkaline solutions (pH 12) lead to the formation of different radicals and solvated electrons (e aq ). Some reaction rates were determined and probable reaction mechanisms were postulated

Monte Carlo simulations of a system of 200 water and 24 NaCl molecules at 6 different densities in the range from 0.003 g/cm3 to 0.999 g,/cm 3 and T = 125 °C and 225 CC were performed to obtain some insight into cluster formation which should precede and determine the formation of aerosol structures and has possibly played some role in prebiotic atmosphere chemistry. Solute hydration occurs already at very low concentrations mainly in the form of hydrated molecules ("contact ion pairs"). At higher densities larger cluster structures are observed, leading rather continuously to the structure of the supersaturated 7.1 M NaCl solution at the same temperature. Radial distribution functions, coordination numbers and particle interaction energies are discussed with respect to the simulation parameters density and temperature

Monte Carlo simulations for a Cu 2+ ion in infinitely dilute aqueous solution were performed on the basis of a simple pair potential function leading to a first-shell coordination number of 8, in contrast to experimental data. A simple method was introduced therefore, which allows the direct construction of a pair potential containing the most relevant 3-body interactions by means of a correction for the nearest neighbour ligands in the ion's first hydration shell. This procedure leads to much improved results, without significant increase in computational effort during potential construction and simulation

The first (ß) and second (y) electric dipole hyperpolarizabilities are calculated for the ground state of ammonia. All independent components of ß xßy and y xßyö are obtained from the energies of the molecule perturbed by a homogeneous electric field. The values of y xxxx , y xxxz , y xxzz and y zzzz are 1232, -106, 1077 and 4319 e 4 a 4 0 E h -3 respectively

The 79 Br and 127 I nuclear quadrupole resonance, NQR, spectra of ortho-substituted anilinium bromides and iodides 2-RC 6 H 4 NH 3 ⊕ X ⊖ with X = Br, I and R = CI, CN, C 2 H 5 , NH 2 , and NH 3 ⊕ X ⊖ have been investigated in the temperature range 77 < T/K <420. Phase transitions occur in 2-(C 2 H 5 )C 6 H 4 NH 3 ⊕ Br ⊖ ½H 2 O at Tc= 164 K. in 2-(C 2 H 5 )C 6 H 4 NH 3 ⊕ I ⊖ at Tc = 214 K, in [1,2-C 6 H 4 (N(H,D) 3 )-]2 ⊕ [Br ⊖ ]2 at Tc = 209 K, and in [1,2-C 6 H 4 (NH 3 ) 2 ]2 ⊕ [I ⊖ ] 2 at Tc = 173 K. The NQR data are discussed and compared with NQR spectra of para-substituted anilinium halides

For S, T isomer pairs of kata-annellated benzenoid hydrocarbons the inequality N S min > N T min holds, where N S min and N T min denote the lowest PMO localization energy of the S and T isomer, respectively. This empirical rule indicates that for a given S, T pair normally the S isomer will be the less reactive one