摘要:

Neutron and hard X-ray diffraction measurements on liquid methanol at room temperature are presented at pressures ranging from 1 bar to 9 kbar. Under ambient conditions a complete partial structure factor analysis has been performed. The partial structures are not all in agreement with simulation results. Notably, the data show no sign of a sharp feature in the HO(O/C) partial, implying that the hydrogen between the hydrogen bonded oxygen is less localized than predicted by the standard simulation potentials. The data have been analysed using a continuous random network approach common in the analysis of the structure of tetrahedral network glasses. The pressure-induced change in the scattering intensity is restricted to the momentum transfer range (0 <Q< 2.5 Å−1), i.e., there is no discernible change in sharp real-space structures. Up to 9 kbar the change in scattering intensity scales to a good approximation with the density.

ISSN:0026-8976    

DOI:10.1080/00268970009483276

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Second Kerr effect virial coefficientsBKof H2S have been calculated using our recent molecular tensor theory ofBKfor molecules of nonlinear symmetry. After optimization of the intermolecular potential interaction parameters and molecular quadrupole moment for H2S, the calculatedBKvalues are seen to agree with the experimental values found in the literature to within 10% over the temperature range of the measured data. The components of the quadrupole moment tensor obtained by optimization are not in good agreement with the one set of calculated values reported in the literature.

ISSN:0026-8976    

DOI:10.1080/00268970009483277

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

General expressions used for transforming raw laser-induced fluorescence (LIF) intensity into the population and alignment parameters of a symmetric top molecule are derived by employing the density matrix approach. The molecular population and alignment are described by molecular state multipoles. The results are presented for a general excitation-detection geometry and then applied to some special geometries. In general cases, the LIF intensity is a complex function of the initial molecular state multipoles, the dynamic factors and the excitation-detection geometrical factors. It contains a population and 14 alignment multipoles. How to extract all initial state multipoles from the rotationally unresolved emission LIF intensity is discussed in detail.

ISSN:0026-8976    

DOI:10.1080/00268970009483278

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A revised potential energy function that has been fitted to the latest set of Kebarle and coworkers [1982,J. Am. chem. Soc,104, 1462] entropy and enthalpy measurements atT= 300 K is presented. The model assumes a rigid hydronium unit and accounts for all orders of many-body interactions explicitly. The difference with the older function that had been based on earlier measurements by Kebarle and co-workers [1972,J. Am. chem. Soc,94, 7627; 1967,J. Am. chem. Soc,89, 6393] is that more compact clusters are generated. We have studied the structural properties of water clusters in the size range 5–80 atT= 250 K within the framework of the (μPT) Grand Canonical ensemble. Clusters with sizes less than about 10 water molecules consist of a four-coordinated first shell, where the fourth water molecule is hydrogen bonded to the oxygen atom of the hydronium ion. The hydration number goes through a minimum value ∼1.6, for a cluster size around 50, and it starts increasing again with further cluster growth, to ∼2.5 for a cluster size of 250 water molecules, which is the largest cluster examined. On the other hand the water molecule coordination number shows a monotonic increase with cluster size. In small clusters, less than 10, water molecules prefer to be arranged in a chain-like fashion; at sizes around 50, tri-coordinated clathrate-like structures dominate whereas with further size increase the coordination number eventually levels off to the experimental bulk value, at 4.6.

ISSN:0026-8976    

DOI:10.1080/00268970009483279

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The use of rotational-resonance experiments to achieve homonuclear polarization transfer between half-integer quadrupolar spins is proposed. We give a theoretical description for a homonuclear two-spin system in the framework of Floquet theory. Numerical simulations, as well as analytical Floquet calculations, were performed to analyse the behaviour of such a system. In most cases of practical relevance, the polarization transfer between the levels involved in the central transitions of the two coupled spins can be described by a pseudo-spin-1/2 formalism. While a rotational-resonance experiment at fixed spinning speed leads only to a partial polarization transfer, an adiabatic passage through the rotational-resonance condition, achieved by a spinning-speed ramp, promotes polarization transfer for all components of the second-order quadrupolar broadened line shape.

ISSN:0026-8976    

DOI:10.1080/00268970009483280

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The effects of range and geometry of a simple attractive square-well on the phase diagram of hard ellipsoids and hard spherocylinders is systematically studied using a simple van der Waals type theory. The orientational single particle distribution function is approximated using the Onsager trial function. The quantitative errors introduced by this are thought to be considerably smaller than the use of the van der Waals approximation, which has been shown to give qualitatively correct phase diagrams for similar models. The phase diagrams obtained for hard ellipsoids and hard spherocylinders of aspect ratios ranging between 3 and 10 with a variety of square-well attractions are found to fall into three general types. The first type shows liquid-vapour coexistence and an isotropic-nematic transition, which meet at a liquid-vapour-nematic triple point. The second type shows a marked widening of the isotropic-nematic biphasic region which pre-empts the liquid-vapour coexistence. The final phase diagram shows a strong destabilization of the nematic phase with respect to the isotropic, which results in a shift of the phase transition to higher densities and pressures as the temperature is lowered.

ISSN:0026-8976    

DOI:10.1080/00268970009483281

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor