ISSN:0005-9021    

DOI:10.1002/bbpc.19840880202

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

年代:1984

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880203

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

年代:1984

数据来源: WILEY

摘要:

AbstractJost's [1] treatment of generalized first order kinetics is used for a new discussion of the mechanism of reversible unimolecular reactions. A detailed analysis of time dependent average microscopic rate coefficients and level populations is presented using exact solutions for a realistic model of an isomerization reaction. It is shown that unimolecular fall‐off for the macroscopic relaxation is not mainly due to a reduced population of reactive levels as suggested by the irreversible Lindemann mechanism, but rather due to a fast reverse reaction even at early times. It is furthermore shown that the average microscopic rate coefficients can be measured directly, in principle. At equilibrium they are equal to the canonical (“high pressure”) limit of the rate coefficient even for arbitrarily low pressures. Practical experimental schemes are suggested for thus obtaining high pressure limiting rate coefficients without extrapolation proce

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880204

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

年代:1984

数据来源: WILEY

摘要:

AbstractAn equation of state reported previously is further developed for the calculation of thermodynamic excess functions in mixtures. The only mixture quantity used is the excess volume. With this quantity, one of the two mixing rules is determined. For the second rule, a plausible, but essentially empirical prescription is applied. Numerical calculations are carried out for the system benzene + cyclohexane.

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880205

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

年代:1984

数据来源: WILEY

摘要:

AbstractLight scattering and differential refractometry at 546 nm have been used to determine Rayleigh ratios, depolarization factors, and refractive index increments in the title systems, at 25°C. The activity coefficients and the excess Gibbs function (GE) have been calculated from these measured magnitudes. The results ofGEtogether with literature values ofHEare used to discuss the importance of interactions and of order in these systems. The mixtures here studied are cosolvent of polymers. The present results should be useful for a better understanding of such phenomenon of cosolvency

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880206

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

年代:1984

数据来源: WILEY

摘要:

AbstractEquilibrium and rate constants of the self‐association of methylene blue and pyronine G in aqueous solutions (water and water/methanol mixtures) are reported for pressures up to 200 MPa atT= 20°C and 30°C. The kinetic measurements were performed in a high pressure cable temperature‐jump apparatus. The volumes of reaction determined from the pressure dependence of the association constants are negative (–9.0 to –13.5 cm3mol−1) for all reactions. From the pressure dependence of the rate constants the volumes of activation are found to be slightly negative for the forward reaction (±0 to –5.3 cm3mol−1) and positive for the reverse direction (+ 4.3 to + 13.3 cm3mol−1). The volumes of reaction of the two intermediate steps of the self‐association (i.e. formation of the encounter complex and rearrangement of the complex to form the dimer) are calculated by using the theory of diffusion controlled reactions. The resulting volume profiles of the reactions are discussed in view of the specific role

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880207

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

年代:1984

数据来源: WILEY

摘要:

AbstractStationary and dynamic fluorescence experiments with pyrene as a probe molecule indicate higher aggregation numbers in Triton‐X‐100 micelles at higher temperatures well below the cloud point. The structure of the micelles is changed considerably as (in spite of higher aggregation) the hydrophobic compartment available to the probe molecules becomes smaller. The increase of aggregation is combined with a decrease of the number of micelles, i. e. micelles are dissolved or merge with oth

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880208

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

年代:1984

数据来源: WILEY

摘要:

AbstractProceeding from the chemical shifts of the13C and27Al atoms, the thermodynamic properties were calculated for the simultaneous formation of the complexes arene · Al2Br6(C) and arene · AlBr3(D) in liquid binary mixtures of methylbenzenes with aluminium bromide. Other stoichiometric models, that take into account the formation of only one complex (C or D) at a time, could only be eliminated by including the27Al NMR data.– We conclude from the effects of concentration on the chemical shifts, that the aromatic π‐electrons transfer charge to the aluminium bromide, which is oriented above or below the aromatic

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880209

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

年代:1984

数据来源: WILEY

摘要:

AbstractKnudsen cell mass spectrometric investigations of the vapour over CsI(s) between 604 and 833 K show the existence of CsI(g), (CsI)2(g), and (CsI)3(g). The enthalpies of sublimation to monomer and to dimer as well as the enthalpy of dimerization are determined with both, the second and third law method, at 298 K as 191.2 ± 2.0, 233.3 ± 4.6 and –149.2 ± 4.4 kJ mol−1, respectively. The values obtained with the second law method at 768 K for the enthalpy of sublimation to trimer and for the enthalpy of trimerization are 256.9 ± 8.3 and –289.9 ± 8.6 kJ mol−1, respectively. Equations for the partial pressures of (CsI)i(g) (i= 1, 2, 3) are given for the temperature range of measurements. The appearance potentials 14.5 ± 0.2(I+), 7.5 ± 0.2(CsI+), 7.2 ± 0.2(CsI+), 12.0 ± 0.2(Cs2I+), 7.2 ± 0.2(Cs2I+), 6.3 ± 0.2(Cs2I2I+), and 7.0 ± 0.2 V (Cs3I2I+) are obtained for the ions given in parentheses which are detected upon vaporizing CsI(s). The obtained findings are compared with data reporte

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880210

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe evaporation of NaI(s) has been investigated by high temperature mass spectrometry and mass‐loss Knudsen effusion experiments with a micro recording vacuum balance. The gaseous phase in equilibrium with NaI(s) consists of NaI(g), (NaI)2(g), and (NaI)3(g). Partial pressures given by the equationslog(pPa) = –(9.479±0.13) 103/T+ 11.49±0.17 for (NaI)(g),log(pPa) = –(10.953±0.06) 103/T+ 12.72±0.06 for (NaI)2(g), andlog(pPa) = –(13.543±0.11) 103/T+ 13.58±0.15 for (NaI)3(g)were determined in the temperature range of the measurements 674 to 843 K. Sublimation enthalpies were obtained in kJ mol−1for the reactionsiNaI(s) ⇄ (NaI)i(g) (i= 1,2,3) (1)as ΔH00= 196.3±4.4 (i= 1), ΔH00= 226.8±1.3 (i= 2), and ΔH00= 284.8±6.6 (i= 3). The enthalpy changes of the dimerization and trimerization reactionsiNaI(g) ⇄ (NaI)i(g) (i= 2,3) (2)are ΔH00= –165.8±8.9 (i= 2) and ΔH00= –304.1±14.8 kJ mol−1(i= 3). The given enthalpy values are averages of the values determined with the second and third law method for each of the reactions Eqs. (1) and (2). Molecular parameters were estimated for (NaI)3(g) and enthalpy increments as well as Gibbs energy functions computed with these data are given. The enthalpy change of the trimerization reaction, Eq. (2) (i= 3), was predicted with Pauling's model for alkali halides as ΔH00= –293.4 kJ mol−1which agrees well with our experimental value. Entropies of sublimation to monomer, dimer, and trimer as well as dimerization and trimerization entropies were obtained at 750 K as 130.1, 148.0, 173.9, –112.2, and –216.4 J mol−1K−1, respectively. Appearance potentials of 8.7±0.1 (Na+), 14.4±0.2 (I+), 8.2±0.1 (NaI+), 8.6±0.1 (Na2I+), 7.5±0.1 (Na2I2+), 8.3±0.1 (Na3I2+), and 8.4±0.1 (Na3I3+) were determined in V for the ions given in parentheses. The data o

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880211

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

年代:1984

数据来源: WILEY