摘要:

Various formulations of the coupled equations in the quantum theory of atom-diatom reactive scattering—based on the ordinary Schrödinger equation and on the generalized equations of the arrangement channel quantum mechanics—are summarized with emphasis on symmetry properties of these formulations. New simplified and/or symmetrized versions are presented of the coupled ordinary differential equations derived previously (using the mixed Jacobi/hyperspherical coordinates) from the two distinct generalized Schrodinger equations which incorporate the arrangement channel permuting and the Fock arrangement coupling scheme, respectively. Inhomogeneous coupled equations arising from the close-coupling description of some related half-collision processes are also included in the considerations. Numerical approaches to solution of the coupled equations problems are recapitulated. The log-derivative method is presented in various versions. The material included in the presentation supplements previous reviews on numerical methods for molecular scattering calculations in that: (i) more information is given on implementations of the invariant imbedding technique; and (ii) determination of scattering wave functions and evaluation of some first- and second-order transition amplitudes involving these functions are considered in addition to determination of the scattering matrices.

ISSN:0144-235X    

DOI:10.1080/01442359309353277

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The fundamentals of the traditional (integrated) light scattering method are reviewed together with the application to a variety of macromolecules of both corpuscular and asymmetric form. Brief mention is made of the application of optical methods to the investigation of particles comparable and larger than the wavelength of the light and of much higher refractive index. Usually termed Mie theory, this involves complex calculations which, in modern instruments, are performed by built-in computers. For much larger particles, Fraunhofer diffraction is available, which can be applied for particle dimensions up to 700 μm. With the introduction of the laser, improvements in traditional light scattering became possible but more importantly, new possibilities arose which made use, particularly, of the coherence properties of laser radiation. Thus dynamic light scattering is concerned with the intensity fluctuations in time which arise from the various possible motions of the scattering particles. Special digital correlators have been introduced to measure the intensity correlation function as the delay time is varied over a large range of values. For spherical particles in dilute solution this gives accurate translational diffusion coefficients and a semi-quantitative measure of the polydispersity for a wide range of particle sizes (from enzymes to viruses). For rod-like particles, in favourable cases, a rotational diffusion coefficient may also be determined and in the case of flexible chain-like molecules, information on the lower order internal modes of vibration may be obtained. For motile micro-organisms, new features on the correlation decay yield a measure of their velocity distribution. All these fields are in active development.

ISSN:0144-235X    

DOI:10.1080/01442359309353278

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In the present review we give an account of dielectric studies under high pressure on plastic and liquid crystalline phases. We emphasize the usefulness of employing hydrostatic pressure as an important parameter for varying the average inter-molecular distance. Furthermore high-pressure studies are indispensable in order to establish the equation of state and the phase diagram for the substance under investigation, let alone that a wealth of phase transitions is only observed at elevated pressures. In the Introduction we outline the basic concepts of mesophases, dielectric theories and experimental procedures. The essential part of the review deals with the presentation of dielectric results for plastic and liquid crystals under high pressures. Both the static and complex permittivity is treated. The latter yields the dielectric relaxation time whose temperature and pressure dependence enables us to derive the activation enthalpy and activation volume, respectively. The dielectric properties of some cyclic and branched alcohols are compared with previous work on the various ice phases. Recent high-pressure studies on some nematic liquid crystals are presented and discussed. The review also briefly notes other dielectric studies under high pressure in neighbouring fields.

ISSN:0144-235X    

DOI:10.1080/01442359309353279

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

This review covers research into the quantum state specific preparation and characterization of highly vibrationally excited molecules, a field of research that has moved into a very exciting period where many new laser techniques can be used to prepare molecules with extremely large quantities of vibrational energy and with exquisite control over the kind of vibrational motion excited. This field gives a foreshadowing of the future, where control of reactant quantum numbers may become as important to the chemist as control of macroscopic reaction conditions such as temperature and pressure. Laser directed chemistry has already been realized in ‘demonstration of principle’ experiments. Many of the unresolved questions relevant to the expanded usefulness laser-directed chemistry will be covered. These include such issues as: (1) control of chemical identity in isomerization reactions, (2) laser-directed photochemical and bimolecular reactions, (3) restriction of intramolecular vibrational redistribution, (4) collisional energy transfer of highly vibrationally excited molecules, (5) atmospheric sightings of highly vibrationally excited molecules and (6) molecular beam scattering of highly vibrationally excited molecules.

ISSN:0144-235X    

DOI:10.1080/01442359309353280

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The effect of intermolecular forces on energy transfer processes, and subtle changes in molecular energy levels can profoundly influence molecular photochemical and photobiological properties. Molecular aggregates isolated under supersonic jet conditions offer opportunities to examine molcular interactions in a way not possible in condensed media, because small, organized arrangements of molecules can be prepared at very low internal temperatures. Many contemporary spectroscopic experiments seek to understand the detailed structures of small aggregates and the potential energy barriers that restrict internal motion. Internal relaxation processes involving conformational rearrangement and microscopic photochemistry in clusters have successfully been time resolved in several cases. At higher energies, vibrational predissoeiation studies convey useful information about the strengths of intermolecular forces. Experiments of this type are constantly being compared with, and offer new opportunities to refine, procedures for structure calculations. One of the most important currently developing areas in cluster spectroscopy involves direct structure determinations. This has involved complementary experiments in both the areas of high-resolution spectroscopy and picosecond time-domain polarization spectroscopy. This combination of structural and dynamical information offers exciting new opportunities to examine photoprocesses on a microscopic scale.

ISSN:0144-235X    

DOI:10.1080/01442359309353281

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor