摘要:

Recent advances in the understanding of the factors which determine line intensities in zero kinetic energy photoelectron spectroscopy (ZEKE-PES) are reviewed. The relative importance of direct ionization and autoionization is assessed. Explicit consideration of the channel interactions which take place in the vicinity of molecular ionization thresholds leads to a general discussion of rotational line intensities in ZEKE-PES. A series of limiting cases is proposed to assist in the interpretation of experimental results. Finally a new dynamical interpretation of ZEKE experiments based on the trapping of the ZEKE electrons in non-penetrating high-lRydberg orbitals by weak electric fields appears to give a satisfactory explanation of most experimental results obtained to date.

ISSN:0144-235X    

DOI:10.1080/01442359309353282

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Results of parameter-free electronic-structure calculations on polymers are discussed. The calculations have been performed using various first-principles density-functional methods. Most first-principles studies have been devoted to finite molecules or infinite, periodic chains. Properties of structural defects which break the translational or helical symmetry can therefore most conveniently be studied by mapping the first-principles results on an adequate model Hamiltonian, which subsequently is used in studying the defects. As examples of applications we examine structural properties of sulphur and selenium helices and compare polyethylene and polytetrafiuoroethylene. We then study in detail trans polyacetylene as the prototype of the conjugated polymers and discuss briefly a number of other conjugated polymers. Hydrogen fluoride is investigated as an example of a hydrogen-bonded polymer and some other hydrogen-bonded chains are briefly discussed. We finally mention other systems that have been or can be treated with the current density-functional methods and conclude by discussing their limitations and possible improvements.

ISSN:0144-235X    

DOI:10.1080/01442359309353283

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

This paper reviews the time-resolved infrared fluorescence technique and its application to studies of the deactivation of highly vibrationally excited benzene-d0, benzene-d6, toluene-d0, and toluene-d8. The energy transfer parameters obtained are summarized in terms of both «ΔE» and <ΔE>d, the average total energy transferred per collision and the average energy transferred in deactivating collisions, respectively. The mechanisms of energy transfer have also been investigated to determine the roles of vibration-to-translation/rotation and vibration-to-vibration energy transfer and the possible influence of quantum effects. The review concludes with a brief summary of a current view of large molecule energy transfer and suggestions for future work.

ISSN:0144-235X    

DOI:10.1080/01442359309353284

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In this review we present a systematic derivation of the multireference coupled cluster theory based on the single reference formalism. The coupled cluster theories have recently emerged as one of the major method development activities in the electronic structure theory of atoms and molecules. Due to its size-extensive nature, using the coupled cluster method the total electronic energy of the system can be determined with the same relative accuracy as the total electronic energies of the fragments which the system separates into in the process of chemical decomposition. This feature is essential for the correct theoretical determination of dissociation energies as well as other molecular properties. One of the most difficult challenges in advancing the coupled cluster theory has been the development of the multireference coupled cluster methodology, i.e. generating a scheme which allows the reference function to incorporate more than one Slater determinant. Such development would enable a very accurateab initiotreatment of general categories of open-shell systems as well as the treatment of systems with stretched multiple bonds leading to a more precise determination of vibrational spectra. In this article we review our recent results in the development of a multireference coupled cluster theory. The reader will be first acquainted with the second quantization formalism, then guided through the derivation of the single reference coupled cluster theory, and finally presented with the multireference formalism. We have included several numerical examples illustrating the performance of the single reference and multireference coupled cluster methods.

ISSN:0144-235X    

DOI:10.1080/01442359309353285

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We present an examination of the H + HX→ H2+Xand H + HX→ HX+ H (X= Cl, Br, I) reactions as a case study of the kind of detailed dynamical information that can be provided by combining thorough experimental measurements with extensive theoretical (computational) simulations. The experimental component is state-to-state dynamics measurement of the absolute cross-sections for reaction from specific quantum states of the HXreactant molecule to particular quantum states of the H2and HXproduct molecules. The interpretation of the quite detailed experimental results is provided by the theoretical component of this work, computational simulations of the reaction dynamics using quasi-classical trajectory calculations. Testing and validation of the quasi-classical trajectory calculations is done by comparison of the state-to-state dynamics theoretically predicted with the dynamics actually revealed in the experiments. When the trajectory calculations are so validated they are used to explore aspects of the dynamics not accessible experimentally and to develop physical models that promote understanding of the dynamics.

ISSN:0144-235X    

DOI:10.1080/01442359309353286

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0144-235X    

DOI:10.1080/01442359309353287

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor