摘要:

Of the twelve possible branches in the 0-0 bands of the forbidden systems A′2Δ-X2Σ+of BaH and BaD, only three are found to be strong [1], namely R12, Q12and Q21. These systems become allowed by mixing of the2Δ state with both the nearby states A2Π and B2Σ+, and interference between transition moments leads to loss of intensity in many branches and to reinforcement in the branches observed to be strong. Semiquantitative agreement with the observed intensity distribution in BaH is obtained if μ‖is taken to be between -μ⊥and -2μ⊥.

ISSN:0026-8976    

DOI:10.1080/00268979100100701

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The Yvon-Born-Green equation under the Kirkwood superposition closure is solved for a system of hard spheres at very high densities, using a robust (second-order) convergence routine. In this paper, the range of the pair correlation function solutions is extended to 100 and 200 diameters. The several solution branches found in an earlier paper (Jangkamolkulchai, A.,Green, K. A., andLuks, K. D., 1989,Molec. Phys.,68,791) were incompletely mapped. These branches are completed for 50 and 100 diameters up to values of λ0= 4πnσ3= 20, where the ‘close packing’ value of λ0is 17·77, and yield multiple results for values of the density parameter λ = λ0g(2)(1 +) on each branch. The interpretation of our results is presented in light of the analysis of solution multiplicity put forth by Lovett for approximate density functional theories.

ISSN:0026-8976    

DOI:10.1080/00268979100100711

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Simulation of collision-induced spectra of gaseous H2-Ar mixtures at 195K taking ternary interactions into account are performed. Interactions are assumed to be pairwise additive. The ternary contribution obtained is in qualitative agreement with experimental results. The central part of the simulated lineshapes narrows with density whereas the wings become enhanced. Both these findings are in accord with experimental observations.

ISSN:0026-8976    

DOI:10.1080/00268979100100721

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We report measurements of depolarized Rayleigh spectra of liquid CS2/CCl4mixtures following the procedure proposed by Cox and Madden and recently used by Hegeman and Jonas. We fit a linear function on two distinct regions of the logarithmic spectra. The slopes Δ depend nonlinearly on the mixture composition. A comparison of our results with those of Hegeman and Jones where we follow the number-density dependence seems to be straightforward for further exploration of our experimental data. Our results indicate that, while in the high-frequency range (region III) of the spectrum changes of pressure and number density have very similar effects, these two parameters affect the lower-frequency range (region II) in a quite different way.

ISSN:0026-8976    

DOI:10.1080/00268979100100731

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In a hard sphere system regions where there is sufficient space to accommodate another sphere are called cavities. Exact relations between the number, size and surface area of cavities, and thermodynamic properties are reviewed, and the prospect of developing a theory of theD-dimensional hard sphere fluid and crystal, and of melting, by analysing the statistical geometry of cavities, is investigated theoretically. The equation of state is expressed aspV/RT= 1 +a(z)/<ν>1/D, wherezis the density relative to close packing,a(z) is a well-behaved cavity shape factor and <ν> is the average cavity size. We show that in the high density limit <ν> varies as (1 -z)DandpV/RTvaries asD/(1 -z). A functionF(z) is defined such that the number of cavities per sphere,nc, is given by lnnc= 1 -pV/RT-F(z) and ln <ν> = ΔS/R- ln(N/V) +F(z), where ΔSis the entropy relative to the ideal gas.F(z) is exactly zero in one dimension, and we show that it is a well-behaved function that tends to a finite constant value in the high-density limit, where lnnc,pV/RT, ln <ν> and ΔSall diverge. These results are used to recover the asymptotic form of the equation of state derived in Salsburg and Wood's polytope theory, but without having to assume the existence of ‘stable close-packed configurations’. They provide expressions for the asymptotic density dependence of <ν> andncand more explicit expressions for the thermodynamic properties at high density.

ISSN:0026-8976    

DOI:10.1080/00268979100100741

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The number and size of the cavities in a hard disc fluid and crystal are calculated in a computer simulation experiment. A cavity is a region where there is sufficient space to insert another disc. In the higher-density fluid and in the crystal the number of cavities per disc,nc, closely follows the exact one-dimensional resultnc= exp(-zpV/RT), wherezis the density relative to close packing, over 40 orders of magnitude. The average size of the cavities, <ν>, varies by only 3·5 orders of magnitude in the same density range, and, to within about 20%, <ν> varies as <ν> = [σ/(pV/RT- 1)]2, where σ is the disc diameter. Across the freezing transitionnc<ν> is exactly constant. When the crystal melts to a fluid the number of cavities increases by about 50% and their size decreases in proportion, but their surface-to-volume ratio only decreases by 5%, showing that they have a more compact shape in the fluid. Above one-half of the close-packed density the computed values ofncand <ν> are represented precisely by lnnc= 1 -pV/RT-F(z) and ln <ν> = ΔS/R- ln(N/V) +F(z), where ΔSis the entropy relative to the ideal gas.F(z) is exactly zero in one dimension, and we find empirically that in two dimensionsF(z) = -0·25 + 2 lnzin the crystal andF(z) = -2·2 - 2 lnzin the dense fluid. The number of vacancies per disc,nv, in the crystal is measured and can be represented bynv=nc/[2(z- 0·75)]. At low density there is a large cavity that percolates. Atz= 0·237 ± 0·003 there is equal probability of a cavity or a cluster percolating. The number of cavities reaches a maximum of one for every three discs atz= 0·38. Relations between cavity, cell and free volume theories are discussed empirically and theoretically.

ISSN:0026-8976    

DOI:10.1080/00268979100100751

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Molecular dynamics calculations of molten salts and soft-sphere binary liquid mixtures have been performed. The self- and cross-correlations of the atomic velocities and displacements are studied from the corresponding time-correlation functions and diffusion coefficients. The effects of both the direct and hydrodynamic interactions on the dynamic cross-correlations as well as their dependence on the reference frame are discussed. The time cross-correlation functions resulting from stochastic simulations by the generalized Langevin dynamics method are also considered.

ISSN:0026-8976    

DOI:10.1080/00268979100100761

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The Lagrangian equations of motion for an infinitely thin vibrating ring and shell are derived, starting from the stretching and bending interactions of molecular force fields. The resulting spectral patterns form useful tools to classify the vibrational levels in annular and globular molecules. They provide a set of parent symmetry labels and predict the relative energetic ordering of the vibrational modes. The method is illustrated for the simple case of the skeletal modes in benzene. The results are compared with the classical treatments of elasticity theory, and with the tensor surface harmonic theory of cluster bonding.

ISSN:0026-8976    

DOI:10.1080/00268979100100771

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The effect of fluid confinement in a narrow cylindrical pore is studied by means of a density-functional approach. An extension of the smoothed-density approximation to the two-component case is employed to explore the structure and phase behaviour of a mixture in a cylindrical pore. Contact is made with the previous local-density treatment and with the macroscopic thermodynamic approach.

ISSN:0026-8976    

DOI:10.1080/00268979100100781

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The dependence of water proton and deuterium transverse relaxation rates on pulse spacing is used to investigate the hydrogen exchange kinetics and water reorientational dynamics in glucose solutions over a wide concentration range. A complementaryT1ρdispersion analysis is also undertaken. The results show that within the pH range 4–8 proton exchange between glucose and water occurs primarily by a non-ionic, cyclic transfer mechanism involving the interaction of two water molecules per glucose hydroxyl group. Interaction with the glucose introduces a slight anisotropy into the reorientational motion of the water. The two correlation times characterizing this anisotropic motion are estimated from the deuterium relaxation data. Similar phenomena are expected in all aqueous carbohydrate systems having accessible hydroxyl groups.

ISSN:0026-8976    

DOI:10.1080/00268979100100791

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor