ISSN:0026-8976    

DOI:10.1080/00268977700102211

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The relaxation of water in aqueous heterogeneous systems is described in terms of the effects of the substrate structure and order on the motions and arrangements of the water molecules. The general observation thatT1is long compared toT2indicates that at least one of the correlation times (τc) is long. A long τccan result from tight binding of some molecules or from the combination of preferential orientation and substrate order. Since doublet splitting characteristic of preferential orientation has been observed for water on a wide variety of organic and inorganic substrate materials, the latter effect might be of general importance in the relaxation phenomena of heterogeneous systems, including biological tissue. For this effect, the conventional 90°–180°T2relaxation curve and the solid-echo curve are calculated for random transitions in a powder sample and for transitions in a gaussian distribution of doublet splitting constants. The results are applied to measurements on clay-water systems to illustrate some effects of structure on transverse relaxation. This application indicates that (a) samples made from oriented clays contain domains characterized by different water contents and different orientations, and (b) the rigidity and domain size and order for powder samples increase with particle size decrease.

ISSN:0026-8976    

DOI:10.1080/00268977700102221

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Molecular structure and order parameters are obtained in this study from nuclear magnetic resonance spectra ofp-fluoro,p-chloro,p-bromo andp-nitrobenzaldehyde partially oriented in EBBA. Reorientation is found to be correlated with rotation of the —CHO group. The angle between the principal order axis and the effectiveC2axis is linearly dependent on the molecular length, indicating that the shape of the molecule is the major factor determining the orientation of these molecules in the nematic phase.

ISSN:0026-8976    

DOI:10.1080/00268977700102231

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

New Monte Carlo estimates of the radial distribution function of a hardsphere solid are given, along with a simple analytic approximation for that function. The approximation is useful over a wider range of densities than that developed earlier by one of us.

ISSN:0026-8976    

DOI:10.1080/00268977700102241

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

A neutron quasi-elastic investigation on a well-orientated chain axis crystal ofn-triacosane has been undertaken using the twin rotor spectrometer on the Pluto reactor at Harwell with an incident neutron wavelength of 2·64 Å. Data taken in the plastic phase show considerable quasi-elastic broadening, both perpendicular and parallel to the chain axis. Good agreement with experiment is obtained using a continuous rotation diffusion model with translational diffusion. On cooling below the plastic phase transition, slight quasi-elastic broadening isalso seen in both configurations.

ISSN:0026-8976    

DOI:10.1080/00268977700102251

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

A general procedure has been developed for constructing analytical potential functions for triatomic molecules which have more than one minimum, these minima not necessarily being related by symmetry. Explicit potentials have been derived for the ground states of HO2, SO2and ClO2. For HO2a linear hydrogen bonded structure O-H----O is predicted as a metastable species. In the case of SO2a second minimum corresponding to the species SOO is predicted andab initiocalculations at the SCF MO double-zeta level have been made to establish the geometry and energy of this. For ClO2it has been assumed that the spectroscopically observed states of OClO and ClOO are separate minima on the same surface.

ISSN:0026-8976    

DOI:10.1080/00268977700102261

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

A truncated Mori expansion for the angular velocity autocorrelation function is used as a starting-point to calculate the orientational auto-correlation function for a disk and a sphere using the newly developed methods of Lewiset al.[9]. Assuming the angular velocity to be a gaussian process, one obtains for a spherical top the first few terms of a development in powers of time. In the free rotor and Debye limits this series can be rearranged to agree with the corresponding terms of the expansion in powers of time of the known limiting expressions. A closed form is obtained for the disk which does the same. It becomes clear that this three-variable Kivelson/Keyes formalism [3] when used for the angular velocity is equivalent to the inertia-corrected itinerant oscillator in two dimensions [24]. Thus it is possible now to relate analytically a realistic, oscillatory angular velocity autocorrelation function to a realistic orientational autocorrelation function for the same molecular symmetry.

ISSN:0026-8976    

DOI:10.1080/00268977700102271

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Coupled equations can serve to determine efficiently and accurately the widths and shifts of levels of diatomic molecules undergoing type I predissociation. A model study has led to a re-examination of a previously given analytical expression for the shift. A corrected expression gives good agreement with the closed coupled results.

ISSN:0026-8976    

DOI:10.1080/00268977700102281

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

We discuss the properties of many-body correlation functions and spectra in liquids, and the corresponding binary (two-body) approximations. We prove that for a general class of triple collisions the many-body and binary spectra become the same at high frequencies; this is illustrated by an explicit model calculation of force spectra and autocorrelation functions. Applications are made to the study of depolarized scattering and to vibrational relaxation in liquids.

ISSN:0026-8976    

DOI:10.1080/00268977700102291

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

New experimental and theoretical work has led to a re-evaluation of the Jahn-Teller effect in ReF6. Low temperature neat and mixed crystal Raman and absorption spectra have been taken. The theory applicable to two Jahn-Teller active vibrations and to a Jahn-Teller molecule in a low symmetry crystalline field is discussed. The main conclusions of the study are that (1) the standard linear Jahn-Teller treatment of vibronically active modes as independent motions characterized by a given vibronic angular momentum is in general inadequate ; (2) Renner-Teller (quadratic) or higher-order vibronic coupling terms are important ; (3) crystal-field splitting of the vibronic levels is not observed ; and (4) vibrational exciton band widths of the Jahn-Teller active vibrations are substantially reduced.

ISSN:0026-8976    

DOI:10.1080/00268977700102301

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor