摘要:

As in the usual interstitial model, disorder is introduced by the displacement of molecules from a bonded ice-like framework onto interstitial sites. However, in this model the interstitial sites are distributed in such a way that its properties can be derived from those of an Ising model on the framework sites. Frameworks considered are the three-dimensional diamond lattice and the two-dimensional honeycomb and square lattices. Accurate liquid/vapour phase diagrams are obtained, density maxima and compressibility minima being found on the liquid branch for appropriate ratios of the non-bonding interaction energy ε to the bonding energyw. Results are compared with those of the zeroth-order and first-order approximations and isobars are calculated using the latter. For the range of ε/wgiving best qualitative agreement between the three-dimensional model and experiment, the first-order and accurate results are very close in the part of the state surface where anomalous water-like properties occur.

ISSN:0026-8976    

DOI:10.1080/00268977500101441

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The inelastic neutron scattering cross section for dense nitrogen gas at several pressures near 240 atmospheres and room temperature has been measured in the region of the first diffraction peak. The Van Hove self-correlation function is calculated from models and subtracted from these cross sections to yield ∂Sd(Q, ω)/∂p. This derivative is related to an integral over the time-dependent triplet correlation function and models for the triplet function are tested. A simple model, based on pair functions, gives moderate agreement.

ISSN:0026-8976    

DOI:10.1080/00268977500101451

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A quantum-mechanical reaction field theory of solvent effects is proposed. It contains as a limiting case Onsager's model. It leads to an effective, non-linear, hamiltonian for the molecule in solution and hence to a tool for studying changes in charge distributions and molecular properties. Numerical examples are given.

ISSN:0026-8976    

DOI:10.1080/00268977500101461

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The1H and13C N.M.R. spectra of a series of imino nitroxide radicals have been studied to obtain electron-nuclei hyperfine coupling constants. A comparison of the spin distribution in these radicals with that previously determined for a series of nitronyl nitroxide radicals indicates a similar mechanism of spin propagation from the heterocyclic ring to the aryl ring, in accord with theoretical predictions [1]. The methyl protons on the two sides of the imino nitroxide ring are found to have different coupling constants: these are discussed in terms of separate interactions with spin at the nitrogen and oxygen atoms. N.M.R. lines are observed from all of the aryl13C atoms and from the α and β carbon atoms of the heterocyclic ring. The aromatic carbon spin polarization parameters are found to be in accord with those previously reported [2]. Polarization of the bridgehead-ortho bond by spin in the heterocyclic ring appears to contribute to the coupling constants of the ortho carbon atoms.

ISSN:0026-8976    

DOI:10.1080/00268977500101471

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Expressions are given for the longitudinal and transverse relaxation rates of the individual lines in a HRNMR proton AX2spectrum. The relaxation mechanisms considered are dipolar and scalar interactions. Measurements are performed on the proton spectra of dilute degassed solutions of 2-amino pyrimidine in acetone-d6/D2O. The relative values are determined of the interproton distances in the AX2system and of three rotational diffusion constants,Dxx,DyyandDzz. Two coupling constants between the ring protons and the14N ring nitrogens are found to be 10·3 and 2·2 Hz.

ISSN:0026-8976    

DOI:10.1080/00268977500101481

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A 16-parameter force field for OCS based on curvilinear coordinates is presented in table 2 and the agreement between observed and calculated transitions and rotational constants is indicated in tables 4, 5 and 6. The computational approach differs from that of Morino and Nakagawa [2] and similar work on other molecules by other authors, in that perturbation theory is eschewed and the calculated vibrational transitions and rotational constants are derived via the numerical solution of a large matrix. The usual parametersxij,yijk, αiBand γijBare thereby rendered inappropriate intermediates. The approach also leads to estimates ofBe-B0for each isotopic species and thence suggests equilibrium distancesrCO= 1·155386(21) Å andrCS= 1·562021(17) Å.

ISSN:0026-8976    

DOI:10.1080/00268977500101491

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

It has been observed experimentally that circular dichroism bands can appear at absorption frequencies of achiral molecules when chiral species (which do not associate with the achiral molecules) are added to the solution. This paper treats those contributions to the induced activity in the achiral species which are the results of van der Waals coupling to the chiral species. Use of perturbation theory leads to the expression of the induced rotatory strength as a series in 1/r,rbeing used in a general sense as the effective achiral-chiral molecule separation. Averaging over all orientations of each molecule yields non-vanishing terms falling off as 1/r6. The results suggest that the effect may be important even in completely dissociated systems.

ISSN:0026-8976    

DOI:10.1080/00268977500101501

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A procedure is developed for the construction of a complex potential in a generalized semiclassical optical model for molecular collisions involving internal nuclear degrees of freedom. The procedure involves a local approximation on the exact quantum optical potential, which is an integral operator over an energy-dependent, non-local kernel. The resulting potential for the model is velocity-dependent. The classical limit of transition amplitudes is obtained from complex-valued classical trajectories whose equations of motion are derived with this potential. The potential contains coordinate integrals over the kernel, and various approximations for the kernel are discussed. Sample calculations are carried out for collinear atom-diatom collisions.

ISSN:0026-8976    

DOI:10.1080/00268977500101511

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Single-crystal E.S.R. studies of Cu(II) diethyldiselenocarbamate and Cu(II) diethyldithiocarbamate, diluted in the corresponding Zn(II) complexes, are reported. The pure copper and zinc crystals consist of dimeric units. When copper is built into the zinc lattice, dimers are formed with one copper and one zinc atom. Theg-tensor, the metal hyperfine and quadrupole coupling tensors and also the hyperfine coupling tensors of the ligand selenium atoms have been obtained. Especially, from the measured selenium hyperfine couplings, it could be concluded that the guest molecules do not accept the structure of the host crystal, but have a structure similar to that of the pure copper compound. This is in contrast to the situation in systems where monomeric host crystals (e.g. nickel (II) complexes) are used and where it is found that the guest molecules do accept the structure of the host. As in the monomeric diselenocarbamate systems, in these dimers the principal axes of thegand metal hyperfine coupling tensor do not coincide. In the dimers a rotation of the hyperfine principal axes has taken place in the plane of the molecule, while a rotation of theg-tensor axes in a plane perpendicular to the molecule is typical for the monomeric systems.

ISSN:0026-8976    

DOI:10.1080/00268977500101521

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The spin hamiltonian parameters of Cu(II) diethyldiselenocarbamate and Cu(II) diethyldithiocarbamate, diluted in the corresponding Zn(II) complexes, have been calculated from the results of extended Hückel Molecular Orbital calculations and compared with the experimentally obtained values (part III). The calculations confirm the conclusions which were drawn from the experimental data: the dimeric units with one copper and one zinc atom do not accept the structure of the host crystals, but have a structure which resembles very much the structure of the pure copper complexes. The rotations of the various principal axes relative to each other in the molecular plane can be understood from these calculations and appear to be caused by a strong mixing of atomic orbitals.

ISSN:0026-8976    

DOI:10.1080/00268977500101531

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor