摘要:

Measurements of the electrical conductivities of liquid and supercooled liquid KCl-glycerol solutions between + 50·6°C and -89·1°C are described. Time domain measurements of dielectric relaxation in pure glycerol between -78·1°C and -91·0°C, and in KCl-glycerol solutions between -77·5°C and -89·1°C are also described. Empirical equations are presented which in each case describe the non-Arrhenius temperature dependence over more than 12 decades in value with a r.m.s. deviation of less than 15 per cent. A ‘power law’ fit is found to be slightly better than a ‘Vogel-Tammann-Fulcher’ fit in each case. The temperature dependence of Walden product for KCl-glycerol solutions is discussed, and the relaxation data for pure glycerol is discussed in the light of the Kauzmann paradox.

ISSN:0026-8976    

DOI:10.1080/00268978400101371

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The low frequency dielectric permittivity has been measured in the different crystal phases of t-butyl chloride, bromide and cyanide. The results have been analysed using model calculations of restricted rotation of the dipole and it has been possible to estimate the effect of preferred orientation of the crystallites in the sample. By comparing the dielectric constant results with those from incoherent quasielastic neutron scattering, it has been possible to establish the nature of the molecular motions in the intermediate phases of t-butyl chloride and bromide.

ISSN:0026-8976    

DOI:10.1080/00268978400101381

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

In this paper the nature, the characteristics, and the potential applications of the optogalvanic effect are explored in a broad set of experiments. The optogalvanic effect was investigated, for the Ar, Ne, He, Ar+, He+, Cu and Na atoms and N2, H2, CO, CN, NH2, He2, and CuO molecules in recombination-limited hollow cathode plasmas, with the use of dye lasers. Comparative studies of the time dependence of transitions from metastable and non-metastable states of neutrals and non-metastable states of ions were made. Autoionizing transitions in Cu(I) were found to yield very strong OGE signals. An examination of the various processes known to be important in such plasmas indicates that associative ionization is a very effective means for coupling light energy into the plasma. Measurement of Rydberg transitions in the helium dimer suggests that optogalvanic spectroscopy in recombination plasmas may be useful as a way to study such molecules with repulsive ground states by generating them ‘from the top down’ by recombination.

ISSN:0026-8976    

DOI:10.1080/00268978400101391

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

An expression is given for obtaining an effective intermolecular potential, which is a function of thermodynamic variables, by averaging over statistical variables that are not of interest. It arises in McMillan and Mayer's theory of solutions, but includes also the methods of taking orientational averages, of including weak three-body potentials in effective two-body potentials, of transcribing the grand partition function of ac-component system to one of a system of (c- 1) components, and is closely related to a generalization to an arbitrary set of molecules of the potential distribution theorem of the grand canonical ensemble.

ISSN:0026-8976    

DOI:10.1080/00268978400101401

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

We have calculated the surface tension σ of the non-critical interfaces which occur near the critical end point for liquid-liquid phase separation. Our calculations are based on a non-local, two-density, mean field approximation to the free energy functional. For both liquid-gas and solid-liquid non-critical interfaces we find that σ and its temperature derivativedσ/dTare continuous at the critical end point. If, however, our results are plotted on an unexpanded temperature scaledσ/dTsometimes appears discontinuous. Our analysis suggests that experiments aimed at testing the prediction thatdσ/dTis continuous will have to be performed at temperatures closer to the critical end point than those performed hitherto.

ISSN:0026-8976    

DOI:10.1080/00268978400101411

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

We have developed a statistical-mechanical theory for the interfacial properties of molecular fluids characterized bystrongly anisotropicpairwise potentials. The theory, which is a generalization to molecular fluids of the mean-field (or van der Waals) theory for the Helmholtz free energy of non-uniform fluids of spherical molecules, was applied to the nematic-isotropic and nematic-vapour interfaces of a simple model of a nematic liquid crystal. Our model exhibits three fluid phases—a nematic, an isotropic liquid and a vapour—which can co-exist in pairs, and which also simultaneously co-exist at a low temperature triple point,Ttr. We present explicit results for theglobalphase diagram of the model which are in good qualitative agreement with data on real liquid crystals.

ISSN:0026-8976    

DOI:10.1080/00268978400101421

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

We have used the theory developed in the previous paper to study the induced orientational order at simple models of a solid-liquid crystal (LC) interface. The LC is modelled by a Maier-Saupe type of anisotropic pairwise potential while the solid is modelled by an impenetrable wall which exerts an anisotropic external potential on the fluid molecules. Our theory treats both the solid-fluid and fluid-fluid potentials on a microscopic level which allows us to study the role played by these two types of interactions in the alignment of the fluid molecules at the solid surface.

ISSN:0026-8976    

DOI:10.1080/00268978400101431

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

We have investigated the hyperfine structure of the υ2=1, (J, K)=(1, 1)-→(2, 1)+mm wave transition and of the ground state (8, 7) inversion transition of14NH3in Doppler-limited resolution. Using additional spectroscopic information from different sources it was possible to determine the υ2=1 effective quadrupole coupling constants. Their values are <1+, 2, 1|eQq|1+, 2, 1> = - (4429 ± 12) kHz and <1-, 1, 1|eQq|1-, 1, 1> = - (4263 ± 18) kHz.

ISSN:0026-8976    

DOI:10.1080/00268978400101441

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

We estimate the importance of the three particle and higher order correlations in two density functional approaches respectively based on the Alastuey-Levesque expansion, and the density gradient expansion which is explicitly computed up to the fourth order term. For that, we study two interface density profiles of the two dimensional, one component plasma. The density gradient expansion is applied to two different uniform backgrounds separated by a permeable line; the Alastuey-Levesque expansion is applied to a flat impenetrable wall. In both cases, various approximations including increasing order correlations are tested in the intermediate coupling regime. The comparison with the analytic and Monte Carlo results shows that the three body effects are rather crucial for the hard wall; the corresponding three body theory is then reasonably accurate. For the soft wall, the familiar square gradient theory, which involves only two body correlations, is very accurate. The higher order correlations do not play an essential role in that case, and even the mean field theories, like the Poisson-Boltzmann approximation, give reasonable results.

ISSN:0026-8976    

DOI:10.1080/00268978400101451

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

We argue that there may be a conceptual difference between calculated (S) and observed (Δ) values of the order parameter in nematics if a mean or molecular field theory is used. Careful definition of the order parameter removes the ambiguity in the case of a Landau approach but a discrepancy remains for molecular field theories. The source of the problem lies in the thermally excited continuum distortions of orientational order which have little thermodynamic effect but may have a large effect on the apparent value of an observable depending on a specific frame of reference. Thus Δ observed by N.M.R., E.S.R. or optical techniques is in fact theS0of molecular field theory after renormalization by thermal fluctuations. This renormalization is estimated in terms of the cutoff of distortional modes. The arbitrariness involved in the use of continuumandmolecular approaches can be circumvented in an operational way. The coupling between local and continuum modes is introduced via a detailed discussion of depolarized light scattering at high temperatures which could help delineate the validity of continuum theory. Motional narrowing in N.M.R. and E.S.R. is discussed. In fact the extraction from N.M.R. of a cutoff length for the spectrum of thermal fluctuations may further help in the estimation of the renormalization. Experiments indicate that this length is of molecular dimensions, a consequence of which would be the use ofS02(and its associated temperature dependence) instead of Δ2in scaling the spin lattice relaxation times observed.

ISSN:0026-8976    

DOI:10.1080/00268978400101461

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor