Showing papers in "Annual Review of Physical Chemistry in 1981"

Many-Body Perturbation Theory and Coupled Cluster Theory for Electron Correlation in Molecules

Abstract: Ten years ago in the Annual Review of Physical Chemistry. there was a review article entitled "Many-Body Theories of the Electronic Structure of Atoms and Molecules," by Karl Freed ( 1 ) . In that article many-body methods were defined to be those techniques which derive their impetus from theories of the N-body problem for which N --+ 00. For the purposes of this review, we further specify these methods as many-body perturba­ tion theory (MBPT) (2-5) and the closely related coupled-cluster meth­ ods (CCM) (6-9) . In the ten years since that review appeared, probably no area in theo­ retical chemistry has undergone more development than has the theory, methodology, and applications of such ab initio many-body methods for

Transition state theory

Abstract: 1. significant progress with the variational formulation of classical TST, in which the objects of interest are "generalized transition states"; 2. the study of quantum analogues of these generalized transition states, which has led to a practical and reliable rate theory for atom-diatom reactions; 3. the development of a quantum TST that avoids the separability ap­ proximation of conventional TST; 4. the use of the TST "line of no return" idea as an aid in the calculation of reaction rates from individual initial states; 5. the invention of an interpolating theory to connect the TST rate ex­ pressions for "direct" and "complex" reactions; 6. the use of variational TST to calculate capture cross sections in ion­ molecule reactions; 7. the resolution of a few questions concerning transition state symmetry.

Quasiperiodic and stochastic behavior in molecules

Abstract: The extent and rate of intramolecular energy transfer play a role in a variety of problems in chemical dynamics. Examples are unimolecular reactions (1 a,b), chemical activation (2a,b), vibrational-rotational-translation energy distribution of the products of a dissociating species (3, 4), infrared multiphoton decomposition of molecules (5a,b, 6), internal conversion and intersystem crossing of electronically excited states (7a-d), dissociation of vibrationally excited state-selected van der Waals complexes (8), fluorescence spectra of electronically and vibrationally excited molecules (9a,b, 10a,b), chemiluminescent spectra of vibrationally excited molecules (11), reactions induced by excitation of high overtones of a bond vibration (12a-c), and high overtone spectra (13a,b). The present article reviews recent theoretical studies on the quasiperiodic and chaotic dynamical aspects of vibrational states and describes how those studies may be related to intramolecular randomization.

Thermodynamic anomalies at critical points of fluids

Abstract: The liquid-vapor transition in a pure fluid and the liquid-liquid transition in a partially miscible liquid mixture are examples of phase transitions that have critical points. These systems exhibit striking macroscopic phe:. nomena near their critical points. Thermodynamic fluctuations within a single phase extend over larger regions of space and become increasingly long-lived as the critical point is approached. For example, near a liquid­ vapor critical point, liquid-like fluctuations within the vapor phase and vapor-like fluctuations within the liquid phase become large enough to scatter significant amounts of light. Thus, fluids which are transparent in all other thermodynamic states become turbid near the critical point, a phenomenon known as critical opalescence. A characteristic size of the fluctuating regions is called the "correlation length" and is given the symbol �. The correlation length diverges toward infinity as the critical point is approached. In the last decade we have come to understand that the divergence of the correlation length is com­ mon to critical points in a plethora of systems: fluids, ferromagnets, fer­ roelectrics, superconductors, etc. It has been exciting to see that this common feature forms the basis for a quantitative understanding of criti­ cal phenomena in such a wide variety of systems.

Electrolyte Solutions at Equilibrium

Abstract: This chapter describes statistical—mechanical tools for the study of ionic solutions at equilibrium. We have attempted to cover those topics which are essential to prospective workers in the field, assuming only that the reader is familiar with the main features of grand ensemble theory, including spatial distribution functions.(1–3)

Gas-Surface Interactions Studied with Molecular Beam Techniques

Abstract: determina­ tions of the gas-surface physisorption potential for several systems have been obtained from surface resonant scattering. The interpretation of dif­ fraction intensities in terms of the geometric structure of the outermost exposed surface atoms now appears capable of being a quantitative struc­ tural tool. The dispersion of surface Rayleigh phonons has been com­ pletely determined for a few surfaces using atom scattering, to an accuracy which has required the theoretical spectrum to be recalculated. The coupling between rotational quanta and surface phonons has been characterized. The details of the average energy transfer between atomic gases and surfaces have been determined and successfully modeled. The partitioning among different scattering channels of particles that undergo energy exchange with surfaces has been studied, as have been the energy distributions of products of several chemical reactions on surfaces. Re­ cently developed techniques have been incorporated into the ultrahigh vacuum (UHV) arrangement normally required for fruitful study. These highlights and a large number of other informative studies with similar objectives form the subject of this review. In general the work surveyed has in common the utilization of molecular (atomic) beam techniques to characterize the details of elastic, inelastic, and reactive encounters of gases with surfaces. Other experimental work may be included if it is

Interstellar Chemistry: Exotic Molecules in Space

Abstract: The field of interstellar chemistry had its beginnings in 1968 with the microwave detection of the first interstellar polyatomic molecule, ammonia. Since then over 50 species have been identified in space (Table 1) (1). Before this it had been thought that molecular processes (as opposed, for example, to atomic and nuclear processes) played little or no role in astrophysics. The wealth of molecular radioastronomical data that has accumulated in the last decade demonstrates quite forcefully that this is not true. Analysis of this data requires information about a number of molecular properties and processes which fall traditionally into the area of physical chemistry. However, because conditions in interstellar space are so different from those which are normally attained in the laboratoryessentially zero pressure and nearly zero temperature-attempts to understand interstellar chemistry have stretched the limits of current physical chemical knowledge. The flow of information between molecular radioastronomy and physical chemistry has therefore been reciprocal, and it is likely to remain this way for some time. Although still quite young, the field of interstellar chemistry has uncovered a remarkably rich and varied phenomenology that has already made important contributions to our understanding of both astronomy and chemistry. In fact, the field is much too broad to be adequately surveyed within the space limitations of this article. Molecular radioastronomical observations have provided important new information for astrophysics, including the morphology and thermal balance of the interstellar medium, clues to stellar evolution, and information about cosmic isotope ratios that

Simulation of Polar and Polarizable Fluids

Abstract: Th« subject of this review is the present status of computations of the dielectric properties of fluids, both static and dynamic, including the closely allied field of light scattering. Although this subject is a very old one, it is far from settled. Over the years many controversies have arisen, primarily because of the need to be careful about the treatment of the boundaries of the system due to the long-range nature of the polar forces. Starting with Nienhuis & Deutch (1), careful work by several theorists has now resolved questions about the formalism for the static equilibrium dielectric properties. reviewed recently by Wertheim (2) in the Annual. Review of Physical Chemistry, and for the dynamic properties, reviewed a