摘要:

The one-electron properties and the components of the polarizability tensor of the nitrogen molecule are calculated as functions of internuclear distance using both SCF and CI wavefunctions. The one-electron properties considered are the quadrupole and hexadecapole moments, the electric field gradient at the nitrogen nucleus and the diamagnetic contributions to the magnetizability and the nuclear magnetic shielding constants. The derivatives of these properties and their dependences upon vibrational quantum number are calculated. The CI values of the one-electron properties are compared in detail with the available experimental data, with particular regard to the accuracy of the methods of determining the multipole moments. The CI results for the polarizability and its derivatives are in excellent agreement with experimental data; however there are serious deficiencies in the SCF results and the results of studies on other molecules suggests that this may generally be the case.

ISSN:0026-8976    

DOI:10.1080/00268978000100021

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A theoretical analysis is given of the response to a 90x-τ-45y-T-45yr.f. pulse sequence of nuclear spin systems whose spectra are dominated by inhomogeneous distributions of second rank interactions. In particular, the cases of (i) a spin-1 system subjected to a distribution of quadrupole interactions and (ii) strongly dipolar-coupled spin-1/2 pairs are considered. A full analysis is presented for the spin-1 system whilst the case of the dipolar-coupled spin-1/2 pairs is considered by analogy. It is shown that, in contrast to the situation where a uniform spin temperature may be established following the 90x-τ-45ypulse pair, the signal in phase with and following the third pulse, for the cases considered here, takes the form of spin echoes centred att = τandt= (T ± τ) rather than a single signal having the shape of the derivative of the FID and starting att= 0. It is pointed out that, whenever the single crystal spectrum of a spin system consists of highly resolved lines arising from second rank interactions, it is unlikely that a uniform spin temperature can ever be established following the 90x-τ-45ypulse pair in a polycrystalline sample. In addition it is noted that there is a complete analogy of the response to the 90x-τ-45y-T-45ysequence of systems with inhomogeneous distributions of second rank interactions with that to the 90-τ-90-T-90 sequence (the Hahn stimulated echo sequence) of systems with a distribution of first rank interactions (e.g.B0inhomogeneity). Experimental measurements on the deuterons in solidd6-dimethylsulphoxide and on the protons in a powder sample of gypsum are presented which confirm the predictions of the theoretical analysis.

ISSN:0026-8976    

DOI:10.1080/00268978000100031

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The Ornstein-Zernike (O-Z) equation for a multicomponent mixture of Yukawa fluids is solved by use of the Wiener-Hopf factorization method developed by Baxter, within the mean spherical approximation (MSA). The fluid-surface interface is then studied through the use of a limiting procedure on a binary mixture, namely, one component is extremely low density but very large radius. Systematic numerical studies of the wall density profile at different points in thermodynamic phase space are given, and these results confirm the monolayer and multilayer structures found by Monte Carlo methods, provided that the coexistence regions of phase space are avoided. Inside the coexistence regions the integral equations apparently give unphysical solutions.

ISSN:0026-8976    

DOI:10.1080/00268978000100041

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Results, which supplement those of Thompsonet al.(preceding paper), are given for a Yukawa fluid interacting with a hard planar wall with an exponential tail. It is argued that density profiles calculated in a mean spherical approximation treatment of this system are only qualitatively reliable.

ISSN:0026-8976    

DOI:10.1080/00268978000100051

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The transition amplitudes for passage through a potential curve crossing are calculated by means of the first order Magnus approximation to the coupled equations in the momentum representation, together with a semiclassical mapping prescription. The cases of potentials with similar or different slopes at the crossing point require a different treatment: for similar slopes the semiclassical Magnus approximation is practically identical with the exponential uniform distorted wave approximation (EUDWBA); for slopes with different signs a new probability conserving approximation is obtained, which differs from the EUDWBA and leads to a substantial improvement of the transition probabilities in the weak and intermediate coupling region. The present approximation can easily be extended to multistate crossings.

ISSN:0026-8976    

DOI:10.1080/00268978000100061

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A formalism based on a linearization procedure is used to obtain an expression for the thermodynamic potential of a system of fluid particles in terms of the local particle number density and bulk structure factor. For the case of adsorption of particles at a single impenetrable interface, minimization of the thermodynamic potential yields an integral equation for the number density identical to that obtained by Percus. From the thermodynamic potential for our model we obtain the force/unit area between two plates which is simply related to the surface density of fluids at the plates. The equations are solved numerically for the one-dimensional hard rod fluid and the three-dimensional Percus-Yevick fluid. The resulting density and force show pronounced oscillations in agreement with recent Monte Carlo calculations. The magnitude of the force is comparable to van der Waals interactions and can thus modify significantly forces that exist between colloid particles.

ISSN:0026-8976    

DOI:10.1080/00268978000100071

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

An independent systems model for the electrostatic crystal field of a lanthanide (III) ion in a crystalline or molecular environment is developed. The two leading multipolar interaction terms retained in the model are the lanthanide multipole-ligand net charge and lanthanide multipole-ligand dipole terms. The former interaction is the basis of the familiar point charge crystal field model. The latter interaction can be expressed in terms of a potential that depends upon the polarizability of the ligands. The combination of the point charge and polarizability crystal fields is the independent systems crystal field (ISCF). Calculations of the ISCF for Pr3+, Eu3+and Tb3+in the Cs2NaLnCl6crystal system are reported. The calculations show that the point charge and polarizability components of the ISCF are of comparable magnitude. Excellent agreement between the calculated and observed crystal field coefficients is obtained for these systems.

ISSN:0026-8976    

DOI:10.1080/00268978000100081

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The details and difficulties underlying the calculation of the symmetry coordinates of an icosahedral molecule are explained in detail and applied to an icosahedral cage. The force field chosen is conceptually very simple and depends on a simple stretching force constantk1which is found to be 144 N m-1for the cage of boron atoms in [B12H12]2-and two bending constants which are -42 N m-1for adjacent bonds (60° bond angle) and +33 N m-1for non-adjacent bonds (108° bond angle). The frequencies of the forbidden fundamentals are predicted with an error which is not expected to exceed ±50 cm-1and which compare favourably with previous predictions.

ISSN:0026-8976    

DOI:10.1080/00268978000100091

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Fully state-selected differential and integral rotationally inelastic cross sections have been determined for the 0 →jtransitions of Li+/H2at a total energy of 0·5 eV. Results have been obtained for space frame, body frame andk1×k2frame quantization. Alignment effects are interpreted in terms of a single rainbow scattering model. A focussing effect due to the anisotropic well is found, confirming conclusions from previous classical trajectory studies.

ISSN:0026-8976    

DOI:10.1080/00268978000100101

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

We have investigated deuterium effects on the ZFS and the sublevel decay rates of3ππ* benzaldehyde in three different hosts. It was found that deuteriation of the formyl hydrogen reduces D considerably in acetophenone and 1,4-dichlorobenzene hosts. This effect is explained in terms of the changes in the3ππ*-3nπ* energy separations.

ISSN:0026-8976    

DOI:10.1080/00268978000100111

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor