This book is concerned with recent experimental and theoretical work dealing with phenomena created by the transient dipoles and polarizabilities produced by intermolecular interactions. The for mer produce absorption from the microwave to the optical regions of the spectrum and the latter produce Rayleigh and Raman scattering; such absorption and scattering would be absent without collisions. Static properties, such as dielectric constant, refractive index, and Kerr effect, also exhibit the effects of induced dipoles and polarizabilities. The first observation of an infrared absorption spectrum pro duced by the collisions of molecules which ordinarily do not have an allowed dipole transition was reported in 1949 (Crawford, Welsh, and Locke). The first observation of depolarized Rayleigh spectra due to collisions in atomic gases appeared in 1968 (McTague and Birnbaum). However, it was not until 1977 that the first conference dealing with collision-induced phenomena was organized by J. D. Poll at the University of Guelph. This conference was mainly concerned with studies of collision-induced absorption in gases. Light scat tering received more attention at the second meeting of the colli sion-induced community in 1978, at the E. Fermi Summer School on "Intermolecular Spectroscopy and Dynamical Properties of Dense Sys tems," organized by J. Van Kranendonk. However, the emphasis was still on collision-induced absorption in compressed gases, although some work on liquids, solid H , and related subjects such as ro 2 tational relaxation was included. The third induced phenomena con ference, organized by F.

Collision-or interaction-induced spectroscopy refers to radiative transitions, which are forbidden in free atoms or molecules, but which occur in clusters of interacting atoms or molecules. The most common phenomena are induced absorption, in the infrared region, and induced light scattering, which involves inelastic scattering of visible laser light. The particle interactions giving rise to the necessary induced dipole moments and polarizabilities are modelled at long range by multipole expansions; at short range, electron overlap and exchange mechanisms come into play. Information on atomic and molecular interactions and dynamics in dense media on a picosecond timescale may be drawn from the spectra. Collision-induced absorption in the infrared was discovered at the University of Toronto in 1949 by Crawford, Welsh and Locke who studied liquid O and N. Through the 1950s and 1960s, 2 2 experimental elucidation of the phenomenon, particularly in gases, continued and theoretical underpinnings were established. In the late 1960s, the related phenomenon of collision-induced light scattering was first observed in compressed inert gases. In 1978, an 'Enrico Fermi' Summer School was held at Varenna, Italy, under the directorship of J. Van Kranendonk. The lectures, there, reviewed activity from the previous two decades, during which the approach to the subject had not changed greatly. In 1983, a highly successful NATO Advanced Research Workshop was held at Bonas, France, under the directorship of G. Birnbaum. An important outcome of that meeting was the demonstration of the maturity and sophistication of current experimental and theoretical techniques.

The Advances in Chemical Physics series provides the chemical physics and physical chemistry fields with a forum for critical, authoritative evaluations of advances in every area of the discipline. Filled with cutting-edge research reported in a cohesive manner not found elsewhere in the literature, each volume of the Advances in Chemical Physics series serves as the perfect supplement to any advanced graduate class devoted to the study of chemical physics.

Chemical Modelling: Applications and Theory comprises critical literature reviews of all aspects of molecular modelling. Molecular modelling in this context refers to modelliing the structure, properties and reactions of atoms, molecules and materials. Each chapter provides a selective review of recent literature, incorporating sufficient historical perspective for the non-specialist to gain an understanding. With chemical modelling covering such a wide range of subjects, this Specialist Periodical Report serves as the first port of call to any chemist, biochemist, materials scientist or molecular physicist needing to acquaint themselves with major developments in the area.

The papers collected in this volume in honor of the late Stanisław Kielich cover an impressive range of modern subjects in molecular science. These subjects include, among others, the nonlinear optics of molecules, new approaches to the electronic structure of large molecules, the properties of carbon nanotubes, fluorescence polarization spectroscopy, computational studies of systems of fundamental interest to collision-induced spectroscopy, the simulation of fluids, NLO materials, chemical bonding in complex molecules, the NLO properties of functionalized DNA and the magnetic properties of molecular assemblies. Written by eminent specialists, the papers should offer valuable guidance to a wide community of graduate students and researchers.

This book introduces systematically the concept of weakly-bound complexes into the broad field of atmospheric sciences. To fill up the gap between our rapidly expanding knowledge of the individual properties of Van der Waals and hydrogen-bonded molecules, and our understanding of their role in the atmospheric processes, an ensemble of related topics are covered by a team of expert co-authors. The general properties of the weakly bound molecular complexes (or “clusters”) are discussed, as well as their distribution in the planetary atmospheres. Collision-induced and dimeric absorption and emission are considered in the context of atmospheric spectroscopy. The advanced experimental techniques which enable us to study the spectroscopic features of molecular complexes in the gas phase, or which are adsorbed, are reviewed. The role of molecular complexes in the cometary atmosphere, the Earth mesosphere, and the atmospheres of the giant planets and some of their satellites are also discussed in detail.

The observable phenomena in liquids ",hich distinguishes this state of matter from other types of condensed matter can be mainly assigned to a) the configurational disorder and b) the random motion of molecules. Both, the static and the dynamic aspect of randomness are typical for the liquid state and serve as a useful guideline in the attempts to theoretically understand this state. These two basic features, however, introduce in liquid state theory a number of apparently unsurmountable technical and conceptual problems so that progress in the last decades has only been made by small steps. In order not to complicate the situation even more, the tacit assumption was made that we could neglect internal motions of the molecules and that the molecular interactions which had to be taken into account are as simple as possible. We thus became accustomed to visualize molecules in the liquid as a dense assembly of classical rigid particles interacting with a potential which basically is represented by a Lennard-Jones type relation. In the last decade, it has become obvious that with these restrictions we dis regard many interesting effects in those liquids which are the most important ones. We thus see a serious gap developing between the refinements of liquid state theory and the exciting experiments being carried out in many laboratories.

Proceedings of the NATO Advanced Study Institute, Luso, Portugal, September 22-October 3, 1991

The new edition will provide the sole comprehensive resource available for non-linear optics, including detailed descriptions of the advances over the last decade from world-renowned experts.

Gas phase molecular spectroscopy is a powerful tool for obtaining information on the geometry and internal structure of isolated molecules as well as on the interactions that they undergo. It enables the study of fundamental parameters and processes and is also used for the sounding of gas media through optical techniques. It has been facing always renewed challenges, due to the considerable improvement of experimental techniques and the increasing demand for accuracy and scope of remote sensing applications. In practice, the radiating molecule is usually not isolated but diluted in a mixture at significant total pressure. The collisions among the molecules composing the gas can have a large influence on the spectral shape, affecting all wavelength regions through various mechanisms. These must be taken into account for the correct analysis and prediction of the resulting spectra. This book reviews our current experimental and theoretical knowledge and the practical consequences of collisional effects on molecular spectral shapes in neutral gases. General expressions are first given. They are formal of difficult use for practical calculations often but enable discussion of the approximations leading to simplified situations. The first case examined is that of isolated transitions, with the usual pressure broadening and shifting but also refined effects due to speed dependence and collision-induced velocity changes. Collisional line-mixing, which invalidates the notion of isolated transitions and has spectral consequences when lines are closely spaced, is then discussed within the impact approximation. Regions where the contributions of many distant lines overlap, such as troughs between transitions and band wings, are considered next. For a description of these far wings the finite duration of collisions and concomitant breakdown of the impact approximation must be taken into account. Finally, for long paths or elevated pressures, the dipole or polarizability induced by intermolecular interactions can make significant contributions. Specific models for the description of these collision induced absorption and light scattering processes are presented. The above mentioned topics are reviewed and discussed from a threefold point of view: the various models, the available data, and the consequences for applications including heat transfer, remote sensing and optical sounding. The extensive bibliography and discussion of some remaining problems complete the text. - State-of-the-art on the subject - A bibliography of nearly 1,000 references - Tools for practical calculations - Consequences for other scientific fields - Numerous illustrative examples - Fulfilling a need since there is no equivalent monograph on the subject