ISSN:0144-235X    

DOI:10.1080/01442358609353367

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The present paper discusses special features in the formation of local vibrations in a crystal having an isotopic defect when these vibrations are in the regions of two and three-particle states of optical phonons and anharmonicity is taken into account. The existence of anharmonicity leads, in some cases, to a cardinal change in the spectrum of local states. Also considered are the conditions for the formation of local biphonons, as well as the available experimental data. Dispersion equations are derived in a number of special cases for triply-bound phonon complexes (triphonons), and conditions are discussed for their localization on an isotopic defect.

ISSN:0144-235X    

DOI:10.1080/01442358609353368

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0144-235X    

DOI:10.1080/01442358609353369

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The application of long-range models to shapes and dipole moments of Van der Waals complexes is reviewed. A simple model incorporating electrostatic interactions through distributed point multipoles, and short-range repulsion through hard spheres, has wide predictive power for the shapes of hydrogen-bonded and other complexes. Successes and limitations of the model are discussed. Inclusion of a distributed polarizability allows semiquantitative prediction of dipole moments of complexes.

ISSN:0144-235X    

DOI:10.1080/01442358609353370

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The topological features of the bare nuclei potential are described in detail. The significance of the impossibility of it having a minimum is discussed. The molecular electrostatic potential and its representation using point charges is then described. The need to have some charges off the nuclei to represent lone pairs and bent bonds is emphasized

ISSN:0144-235X    

DOI:10.1080/01442358609353371

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Molecules with CX3NO, CX3CHO, and related structures have eclipsed conformations in their ground electronic states, but adopt a staggered equilibrium conformation in theirnn*excited states. This dramatic difference in the torsional barrier in different electronic states of the same molecule is an important clue towards a fuller understanding of the relation between electronic structure and preferred conformation. Results to date are reviewed, and suggestions are made for further experimental and theoretical studies.

ISSN:0144-235X    

DOI:10.1080/01442358609353372

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

At high vibrational energies the redistribution of vibrational energy is very rapid in accord with the broad linewidths measured. At low energies, no such consistent picture has emerged. For many systems the line-broadening threshold is at about 1500cm1, yet for others no broadening is observed for thousands of cm−1. Infrared spectra of ethylene dimers are marked by large linewidths whereas lines narrower by several orders of magnitude are observed for the larger molecular dimers benzene and methylacetylene.

ISSN:0144-235X    

DOI:10.1080/01442358609353373

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Overtone spectroscopy, through the local-mode model, can be used to determine CH bond lengths in substituted aromatic molecules. These highly accurate bond lengths correlate remarkably well with geometry-optimizedab initioMO calculations at the 4-21G level. The spectra can also be used to obtain dynamic information on such processes as methyl internal rotation in toluene.

ISSN:0144-235X    

DOI:10.1080/01442358609353374

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Usingab initioself-consistent field molecular orbital methods the validity and potential predictive capabilities of electrostatic methods are explored with specific reference to the determination of the shapes of weakly bound molecular complexes and the changes in electronic properties that occur on the formation of a dimer, cluster or crystal. The Van der Waals dimers (H2O)2, C12-HF, C1F-HF and N2O-HF are studied from the structural point of view while for water other properties, such as dipole moment, dipole moment derivatives and17O nuclear quadrupole coupling constant are also investigated. In all cases, except for the dipole moment derivatives, the electrostatic effects are shown to account for the major part of the observed effects. Finally, the results of a purely electrostatic calculation of the vapour to solid shift of the14N nuclear quadrupole coupling constant in ammonia are discussed.

ISSN:0144-235X    

DOI:10.1080/01442358609353375

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Molecular wavefunctions calculated with basis sets supplemented with higher-order functions show a smooth increase in the degree of d-function involvement from a polarizing role in main group compounds of normal valency to a genuine valence-orbital role in hypervalent compounds; compounds of second-row elements, especially when bonded to electronegative elements, often use d-functions in a marginal valence role. d-Functions contribute to molecular wavefunctions predominantly in bonding; atomic population terms are very small. The absence of orthogonality constraints (the d-functions are nodeless) facilitates the use of dπ-functions to reduce excessive charge disparity built up in the σ-network. Although exponents may he no greater than those found for normal valency compounds, d-function supplementation is often indispensable for the description of the bonding in hypervalent compounds in many of which more than one set of gaussian d-functions may be needed.

ISSN:0144-235X    

DOI:10.1080/01442358609353376

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor