摘要:

AbstractWe have measured the self‐diffusion coefficient and density properties of 15‐crown‐5 and 18‐crown‐6 ethers in aqueous (D2O) and CDCl3solutions in the range of 0 to 6 m concentration of ethers. Some measurements for 1 m crown in D2O with various concentrations of alkali‐metal bromides are also reported. It has been observed that self‐diffusion coefficients of the crowns are small and decrease with increase in concentration of the crown both in D2O and CDCl3solutions. The density data in D2O were used to obtain the apparent molar volumes of the crown φvas a function of concentration. It has been observed that φvgoes through a minimum at about 2 m of crown concentration. Similar measurements and calculations of 1 m crowns in D2O in various salt solutions indicate thatDvaries peculiarly as a function of salt concentration. In case of KBr solutions,Dincreases initially and goes through a flat maximum at about 1–2 m of KBr concentration. The apparent molar volumes of the salts calculated in 1 m 18‐crown‐6 and 1 m 15‐crown‐5 solutions exhibit anomalous dependence on salt concentration. These results are explained on the basis of solute‐solute, solute‐solvent, ion‐crown and ion‐i

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010112

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractRelaxation rates of carbon‐13 magnetization of the C9 carbon positions in two poly‐n‐octyl star‐hydrocarbon oils, 9‐n‐octyl‐n‐heptadecane and 9,10‐di‐n‐octyl‐n‐octadecane, and of deuterium magnetization in 9‐n‐octyl‐n‐heptadecane‐9d, and 9,10‐di‐n‐octyl‐n‐octadecane‐9d1, labelled with deuterium at the same carbon position, have been measured over wide ranges of temperature and at two field strengths. In this paper simulation of the observed relaxation rates within the assumptions of the Lipari and Szabo picture of molecular rotational diffusion, and dipolar and quadrupolar relaxation mechanisms, determined molecular rotational diffusion constants, activation energies, and Lipari and Szabo order parameters and correlation times for internal molecular motion at the labelled positions. The appropriate quadrupolar coupling constants could also be determined from the measured data. The effect of the rate of internal molecular isomerization was discussed and it was shown that in general this had to be included in the theoretical picture in order to derive a consistent set of motional parameters that generated a

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010113

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractSolvatochromic behavior of 2,6‐diphenyl‐4‐(2,4,6‐triphenyl‐1‐pyridinio)‐1‐phenolate (RB), 1‐methyl‐8‐oxyquinolinium betaine (QB), sodium 1‐methyl‐8‐oxyquinolinium betaine‐5‐sulphonate (QBS), and 1‐methyl‐3‐oxypyridinium betaine (PB) was studied UV/Vis spectrophotometrically in binary mixtures of water with methanol, ethanol, 1‐propanol, 2‐methyl‐2‐propanol, ethane‐1,2‐diol, 2‐methoxyethanol, and 2‐n‐butoxyethanoI. The solvent polarity parameter,ET(in kcal/mole), was calculated from the position of the longest‐wavelength absorption band of the solvatochromic probe, and was then correlated with χw, the mole fraction of water in the mixture. Except for PB in aqueous methanol, aqueous ethanol and aqueous 1‐propanol, plots ofETversus χware not linear because of preferential solvation of the probe by one component of the mixed solvent and, when applicable, because of solvent microheterogeneity. In the same aqueous alcohol mixtures, deviation from linearity in theETversus χwplots increases as a function of the increasing hydrophobic character of the probe. For the same solvatochromic probe in different aqueous mixtures, the above mentioned deviation increases as a function of increasing the chain length of the alcohol. Preferential solvation of the probe is described in terms of the so called “solvent fractionation factor, ϕs”, whose value indicates the relationship between composition of the solvation shell of the probe, and composition of the bulk solvent. In the absence of solvent microheterogeneity, all values of ϕsare less than unity, which indicates preferential solvation of the probe molecule by the alcohol. An attempt to evaluate contributions from preferential solvation and solvent microheterogeneity to solvatochromism in aqueous methanol, and aqueous THF showed that the approach used

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010114

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractThe shear viscosity of hexane+tetradecafluorohexane has been determined from five Kelvins below the upper critical solution temperatureTc– in the region of limited miscibility – to 19 Kelvins aboveTc– in the region of total miscibility. The results show a critical anomaly described by a critical expression η =Aexp (B/T)ϵ−ywith a multiplicative amplitude or background term η0=Aexp (B/T) and a weakly anomalous term ϵ−y, where ϵ is the reduced temperature response function |T−T|/Tccalculated withTc= 22.385°C, and the critical exponentytakes the universal value 0.040 predicted by the mode‐mode and renormalisation group theories. The measured viscosities show a definite but small dependence on shear gradient. The shear gradient dependence is entirely described by the Oxtoby treatment which yields an estimate of the critical amplitude of the correlation length ξ0= (5.5 ± 1.5) Å in fair agreement with the light‐scattering value of Skripov et al. of (3 ± 1) Å. The ratio of the limiting amplitudes along the isochoric path and the coexistence path is 0.946 ±0.005, close to that pr

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010115

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractDensity of expanded fluid selenium was measured in the temperature and pressure ranges up to 1650°C and 700 bar including the liquid‐vapour critical point by the x‐ray absorption method. For the measurements, a new type of cell made of polycrystalline sapphire and a high‐pressure vessel of authors' own design were developed. The critical temperature, pressure and density of 1615 ± 5°C, 385 ± 5bar, 1.85 ± 0.03g cm−3, respectively, were obtained. We found that isochores bend in the semiconductor‐metal transition region. The shape of the isochore seems an elongated inverse‐S letter. The diameter of the liquid‐vapour coexistence curve is deviated from the law of the rectilinear diameter to the liquid side slightly around the SC‐M transition region and strongly near the critical point. A distinct crossover was also found in the critical exponent β; the value of β drastically changes from 0.30 to 0.10 when the critic

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010116

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractThe rate constants for the reaction of NCO (X2Π) radicals with NO and NH3were measured at 20 Torr total pressure in temperature ranges of 290–1098 K and 295–882 K, respectively, using ClNCO excimer laser photolysis for NCO radical formation in combination with laser‐induced fluorescence detection of NCO. In the temperature range investigated the NCO + NO reaction exhibits a negative temperature dependence which is described by the following three parameter Arrhenius equation:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{{{\rm NCO}} + {{\rm NO}}} (T) = (1.45_{ - 0.35}^{ + 0.55}) \times 10^{ - 5} \times T^{(- 1.98 \mp 0.06)} \times \exp [ - (3.74_{ - 0.83}^{ + 0.91})/RT/{{\rm cm}}^3 \;{{\rm s}}^{ - 1} $$\end{document}, withE0in units of kJ/mol.For the NCO + NH3reaction the measurements exhibit a positive temperature dependence over the temperature range investigated with a slight upwards curvature. A modified three parameters Arrhenius fit provides a good description of the experimental data:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{{{\rm NCO}} + {{\rm NO}}} (T) = (1.45_{ - 0.35}^{ + 0.55}) \times 10^{ - 5} \times T^{(- 1.98 \mp 0.06)} \times \exp [ - (3.74_{ - 0.83}^{ + 0.91})/RT/{{\rm cm}}^3 \;{{\rm s}}^{ - 1} $$\end{document}, withE0in units of kJ/mol. In addition, the rate constant of the NCO + NH3reaction was found to be pressure independent in the range 10–193 Torr

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010117

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractThe product channels were investigated of the reaction between CH2\documentclass{article}\pagestyle{empty}\begin{document}$$ ({{\rm \bar X}}^3 {{\rm B}}_1) $$\end{document}and NO in the gas phase at room temperature and near ambient pressure. Mixtures of CH2CO/NO/Ar were photolyzed at λ = 312 nm in a static reactor. The reaction products were analyzed by Fourier transform infrared (FTIR) spectroscopy. The main product (≈︁ 84%) was found to be fulminic acid, HCNO. A second channel (≈︁ 15%) was found to lead to HCN. Other products which were detected include CO, N2O, H2O, HONO, H2CO, and CO2. These are formed (except for the CO from the CH2CO photodissociation) in consecutive reactions of the accompanying H atoms and OH radicals from the HCNO and HCN reaction

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010118

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractThe electropolishing ofp‐Si(100) in aqueous NH4F solution is investigated in‐situ by photoluminescence (PL) with short N2‐laser pulses. The PL signal increases with potential and reaches a maximum when current oscillations occur. The PL signal oscillates with the same period but anticorrelated to the current. The thin anodic oxides are removed at a low cathodic potential. The respective peak of the current transient is used to monitor the relative changes of the anodic oxides. The results are discussed from the point of view of non‐radiative defect generation during electropolishing, which is controlled by the potential and the rate of ox

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010119

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010120

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010121

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY