摘要:

In this review the four best techniques that answer the question ‘Given an analytical potential-energy surface, how does one calculate the (J = 0) vibrational energy levels?’ are discussed. The methods examined are (i) the fully variational matrix procedure, (ii) the semiclassical approaches relying on quantisation of the Einstein action integrals, (iii) the adiabatic switch-on method, and (iv) the quantum Monte Carlo method applied to vibrations. In particular, the usefulness of each procedure is examined with regard to the number of atoms (N⩾ 3), and the calculation of highly excited vibrational levels.

ISSN:0144-235X    

DOI:10.1080/01442358909353231

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The special features of synchrotron X-radiation and the types of instrumentation required for a range of synchrotron X-ray diffraction experiments are outlined. A diverse range of applications to inorganic and heterogeneous catalyst systems are discussed. Grazing incidence X-ray diffraction experiments have revealed a number of surface structures and followed surface phase transformations; similar studies of boundary and interfacial structures are cited. Experiments on catalytic metals dispersed on supports have exploited anomalous scattering effects. High-resolution powder diffraction has assisted phase identifications, provided quantitative data on peak broadening (such as arise from particle size effects or stacking disorder), enabled studies of subtle superstructures and a growing number ofab initiostructure solutions, and permitted Rietveld refinements of a range of inorganic materials. The potential for performing measurements on individual crystallites in the micrometre size regime has been demonstrated; a small number of successful single-crystal structure refinements have been described. Single-crystal Laue methods have been also applied successfully to structure refinements and solutions; this configuration potentially permits data sufficient for structure definition to be recorded on a nano-microsecond time scale. A range of studies that are time-resolved (currently on somewhat longer scales), and various studies under non-ambient conditions (such as at high or low temperatures, at extreme pressures, or under applied magnetic and electric fields) have also been described. These various applications of synchrotron X-ray diffraction techniques to inorganic and heterogeneous catalyst systems both illustrate already substantial contributions to our understanding, and promise still greater advances from future applications.

ISSN:0144-235X    

DOI:10.1080/01442358909353232

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Molecular quantum electrodynamics (QED) is the theory of interaction of molecules with radiation. An essential feature is the application of quantum conditions to the radiation; the associated particles, which are the carriers of the momentum and energy, are photons. In QED the electrodynamic vacuum possesses zero-point energy. Fluctuations in the energy of the vacuum state are the causes of phenomena such as ‘spontaneous’ emission and the Lamb shift, and are the source of the virtual photons important in the understanding of intermolecular interactions. In this connection an attractive feature of the theory is its power to deal with the coupling between molecules within the same framework as radiation-molecule interactions, the molecule-molecule effects being mediated by photons, real and virtual. In this review the multipolar form of QED is described, and applications are given with some emphasis on recent work, for example three-body resonance and synergistic effects in two-photon two-molecule processes. After formulation of the theory, applications are outlined with particular reference to one-and two-photon absorption, spontaneous and stimulated emission, natural and laser-induced circular dichroism, field-induced absorption and harmonic generation. Among intermolecular interactions, accounts are given of resonance and dispersion coupling, molecule-induced circular dichroism, and cooperative two-photon absorption.

ISSN:0144-235X    

DOI:10.1080/01442358909353233

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Royal Society of Chemistry Specialist Periodical Reports, Nuclear Magnetic Resonance, Volume 18. Senior Reporter G. A. Webb (Royal Society of Chemistry, 1989.) [Pp. vi + 511.] £110. Isbn 0851864120.

ISSN:0144-235X    

DOI:10.1080/01442358909353234

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0144-235X    

DOI:10.1080/01442358909353235

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor