摘要:

Lattice gases are investigated consisting of several boxes in which any particle interacts only with particles at its nearest neighbour sites within the same box, and particles can hop from one box to the other so that the total number is conserved. Two equal square lattices with attraction between particles in the same plane are simulated using the Monte Carlo method. While the equilibrium properties of this system are related simply to those for the plane, time relaxation differs. There are some interesting consequences, e.g., a consideration of two lattices may permit the more accurate determination of steady state properties in some cases, and novel phenomena may be exhibited. The nature of finite-size effects for low density is peculiar also. Further cases that exhibit interesting behaviour, even for one-dimensional boxes, are studied analytically by means of exact and mean-field solutions.

ISSN:0026-8976    

DOI:10.1080/00268979609484501

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The experimental values of the two lowest spectral moments of the far infrared collision induced absorption spectra of gaseous N2and CO2are compared with results from analytical formulas (A. Borysow and M. Moraldi, 1992,Phys. Rev. Lett.,68, 3686) allowing for the anisotropic intermolecular potential. A purely electrostatic induction mechanism was sufficient to reproduce the experimental values of the spectral moments of N2. For CO2, in order to achieve similar agreement, an overlap contribution to the induction terms was introduced. These new terms provide a correction to the present authors' earlier results (M. Gruszka and A. Borysow, 1994,J. chem. Phys.,101, 3573), where no overlap was used. The impact of the anisotropy of the intermolecular potential on the spectral moments of N2and CO2has been analysed, and also the applicability of perturbation theory for computing the spectral moments. In both cases, N2and CO2, it was found that the perturbation series does not converge, when realistic interaction potentials are used.

ISSN:0026-8976    

DOI:10.1080/00268979609484502

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The kinetics of charge-transfer complex formation between iodine as an acceptor and benzene as a donor has been investigated using Raman spectroscopy. The iodine was dissolved in dilute (0–3 volume %) mixtures of the donor in n-heptane used as an inert solvent. By using low donor concentrations, the non-reactive part of the line profile can be considered constant so that the reactive part of the profile can be separated out from the total lineshape. For this purpose, a two-state Markov process model is presented for the Raman lineshape of the free iodine-complexed iodine system. The model is formulated on the basis of the theories of Kubo, Gordon and Strauss. It predicts that at low donor concentrations the net Raman scattering linewidth grows linearly with donor concentration and that the complex formation causes a Lorentzian contribution to the total line profile, which on Fourier transformation yields an exponential. The logarithm of this function is a straight line, the slope of which is a function of the dissociation rate of the complex. According to the model, the slope is obtained by dividing the absolute value of the transform of the spectrum under investigation with that of a spectrum measured in neat n-heptane. The prediction of a ratio of constant slope is verified accurately by our measurements. The lifetime of the benzene-iodine complex at 300 K is found to be 2·4+0·5−0·4ps usingK= 0·356 1 mol−1(determined by Childs from polyiodide solubility data) for the equilibrium constant of the complexing reaction or 1·2+0·4−0·2ps usingK= 0·203 1 mol−1(spectroscopic value determined by Childs).

ISSN:0026-8976    

DOI:10.1080/00268979609484503

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The kinetics of formation of the toluene—iodine charge-transfer complex has been investigated using Raman spectroscopy of the iodine vibrational line. Using low donor concentrations, the non-reactive part of the line profile can be separated out from the total lineshape with the aid of the inverse Fourier transforms of the Raman spectrum. The remaining part arises in the complex formation and dissociation process only, and can be used to extract the complex lifetime. Spectra were recorded at 300 K from a solution of iodine dissolved in dilute (0–3 volume%) mixtures of the donor in n-heptane used as an inert solvent. Using for the equilibrium constant the value 0·500 l mol−1obtained by Childs using the polyiodide solubility method, the lifetime of the toluene—iodine complex as determined from the residual linewidth of the reactive part of the total line profile is found to be 0·9−0·2+0·3ps. The equilibrium constant value of 0·315 l mol−1obtained by Childs using the spectroscopic method is not consistent with a simple two-state model. The meaning of the concept of the lifetime of the complex is discussed. It is argued that it may describe the influence of several different processes, including both true dissociation of the complex and non-reactive collisions between the iodine and the donor molecules.

ISSN:0026-8976    

DOI:10.1080/00268979609484504

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The lifetimes of the charge-transfer complexes between iodine andx-xylene and iodine andp-xylene have been investigated using Raman spectroscopy of the iodine vibrational line. Using low donor concentrations the non-reactive part of the line profile can be separated out from the total lineshape with the aid of the inverse Fourier transforms of the Raman spectrum. The remaining part arises in the complex formation and dissociation processes only and can be used to extract the complex lifetime. Spectra were recorded at 300 K from a solution of iodine dissolved in dilute (0–3 volume%) mixtures of the donor in n-heptane used as an inert solvent. The lifetime of the iodine—o-xylene complex as determined from the residual linewidth of the reactive part of the total line profile is 0·8 ± 0·2 ps and that of the iodine—p-xylene complex as 0·6−0·1+0·2ps. The results are also discussed in terms of a possible extension of the model to incorporate a transitional state intermediate between the free-iodine molecule and iodine bound in the complex.

ISSN:0026-8976    

DOI:10.1080/00268979609484505

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The charge-transfer complex formation between iodine as an acceptor and durene as a donor has been investigated using Raman spectroscopy. The iodine was dissolved in dilute (0–3 volume%) mixtures of the donor in n-heptane used as an inert solvent. The kinetics of the complex can be simulated with a two-state Markov process model for the Raman lineshape of the free iodine—complexed iodine system. The model is formulated on the basis of the theories of Kubo, Gordon and Strauss. At low donor concentrations the non-reactive part of the line profile can be considered constant so that the reactive part of the profile can be separated out from the total lineshape. This operation is performed using iterative convolution of the Kubo—Gordon lineshape function with a reference spectrum measured at zero donor concentration. The lifetime can then be calculated from the iteratively determined best fit lineshape function. The lifetime of the complex at 300 K is 4·3−1·0+1·5ps.

ISSN:0026-8976    

DOI:10.1080/00268979609484506

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A new method for measuring circular dichroism (CD) is described, based on a transient grating and using spatially modulated right and left circularly polarized light (the TG-CD method). The effects of the optical properties of a sample, e.g., linear dichroism (LD), linear birefringence, circular birefringence, and also of time resolution, sensitivity and solvents are discussed. It is shown that LD, which could be produced by pre-excitation for a time-resolved CD measurement, may introduce errors in the measurment of CD.

ISSN:0026-8976    

DOI:10.1080/00268979609484507

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The Boublik-Mansoori-Carnahan-Starling-Leland (BMCSL) equation of state is examined for binary hard sphere mixtures. It is argued that this equation of state is reliable for a large diameter ratio. Monte Carlo (MC) simulations are performed for many states, some of high density and large diameter ratio. At moderate densities away from the solid-liquid transition, the MC results show reasonably good agreement with the BMCSL's prediction of the compressibility factor. This confirms the earlier findings of Jacksonet al.for the validity of BMCSL in the liquid phase. The failure of the BMCSL prediction in some states is due to proximity to the solid-liquid transition and not due to the large diameter ratio. The individual pair distribution functions predicted by the BMCSL in all cases, however, can be poor, especially, for a pair of large spheres at very low concentration. Comparison of the MC distribution functions and those predicted by several theories are made.

ISSN:0026-8976    

DOI:10.1080/00268979609484508

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The homogeneous colour conductivity problem for a binary mixture in the low-density regime is studied by means of the direct Monte Carlo simulation method. This method is used to solve the Boltzmann equation for three different repulsive r−μpotentials: Maxwell molecules (μ = 4), ‘soft’ spheres (μ = 12), and hard spheres (μ → ∞). The main transport properties and the velocity distribution functions are computed as functions of the field strength and the parameters characterizing the mixture. In the case of Maxwell molecules, the results are compared with those derived from anexactsolution of the Boltzmann equation, showing fairly good agreement over a wide range of field strengths. Beyond the Maxwell interaction, the effect of the interaction potential on the properties of the system is analysed.

ISSN:0026-8976    

DOI:10.1080/00268979609484509

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A novel method for calculating rotational resonance (R2) NMR spectra for dipolar-coupled homonuclear spin pairs is presented. A perturbation approach was exploited in the framework of Floquet theory to approximate the time evolution of the spin states, which is not represented in a closed form. The recurrence formulae for the perturbation corrections were derived and very high-order perturbation terms, such as tenth-order, can be calculated efficiently; the spectra thus calculated in the high-order perturbation treatment are substantially exact when the convergence of the perturbation expansion is assured. The computations of the spectra using the present Floquet formalism are fast, permitting the iterative calculations for determining the optimal spin parameters. Experimental results of theR2spectra as well as the exchange of the Zeeman order promoted underR2conditions are presented and compared with the calculations.

ISSN:0026-8976    

DOI:10.1080/00268979609484510

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor