Reaction dynamics overview

The outline of the chapter is the following. In Sec. 2, we give an overview of GH theory and various important limits, as well as an overview of its applications to assorted charge transfer reaction classes. In Sec. 3, we sketch a model development that is quite useful in comprehending the meaning of GH theory. Various MD simulation studies on reaction dynamics are described in Sec. 4. from the perspective of the preceding sections. Sec. 5 sketches some other related developments, while concluding remarks are offered in Sec. 6. 

I had the honor to review the field, as described by the title of this chapter. I would like to take this opportunity here to focus on some concepts that were essential in the development of femtochemistry reaction dynamics and control on the femtosecond time scale. The following is not an extensive review, as many books and articles have already been published [1-12] on the subject, but instead is a summary of our own involvement with the development of femtochemistry and the concept of coherence. Most of the original articles are given in a recent two-volume book that overviews the work at Caltech [5], up to 1994. 

In this chapter, we will review the reaction dynamics studies which has been performed on supported model catalysts in order to unravel the elementary steps of heterogeneous catalytic reactions. In particular we will focus on the aspects that cannot be studied on extended surfaces like the effect of the size and shape of the metal particles and the role of the substrate in the reaction kinetics. In the first part we will describe the experimental methods and techniques used in these studies. Then we present an overview of the preparation and the structural characterization of the metal particle. Later, we will review the adsorption studies of NO, CO and 02. Finally, we will review the two reactions that have been investigated on the supported model catalysts the CO oxidation and the NO reduction by CO. 

The contribution of Berry presents an overview of the study of clusters as vehicles for investigating complex systems. The study of clusters has given birth to a variety of new ideas which turned out to be fruitful in other complex systems such as proteins. The contribution of Takatsuka discusses dynamical and statistical aspects of phase transitions in clusters, and the contribution of Yanao and Takatsuka studies the gauge structure arising from the dynamics of floppy molecules. Shida s contribution presents an important issue related to saddles of index of two or more, and shows their role in the phase transitions of clusters. Another interesting phenomenon of clusters is fast alloying, discussed in the contribution of Shimizu et al. from the standpoint of reaction dynamics. 

Following a general overview, that summarizes the pioneering role of the LCAP project, o give accounts of work in quantum chemistry, molecular dynamics, and reaction dynamics. Each of these subsections is organized to review the development and current status of codes in the area and to provide an overview of work under way where serial implementations are migrating onto parallel architectures. 

S. A. Rice, Overview of the dynamics of intramolecular transfer of vibrational energy, Adv. Chem. Phys. 47 117 (1981) P. Brumer, Intramolecular energy transfer theory for the onset of statistical behavior, Adv. Chem. Phys. 47 202 (1981) P. Brumer and M. Shapiro, Chaos and reaction dynamics, Adv. Chem. Phys. 70 365 (1988). 

We begin by outlining the task and suggesting why a reaction path approach to evaluating a PES is plausible. Three important technical questions must then be addressed Exactly how do we define a reaction path, how do we calculate it, and how do we use it to describe a PES Because this task lies along the interface between ab initio quantum chemistry and reaction dynamics, even these three technical questions cannot be answered completely without reference to how we intend to evaluate the reaction dynamics. So when we go on to describe how the reaction dynamics is to be studied, we have to return from time to time to the questions of what path and what PES. Without claiming to cover the area exhaustively, we hope to arrive at a reasonable overview of how the simple reaction path approach works in practice. This is an active area of research, and some very useful reviews have already appeared [10-12]. 

Abstract. This paper presents an overview of the time-dependent quantum wavepacket approach to chemical reaction dynamics. After a brief review of some early works, the paper gives an up-to-date account of the recent development of computational methodologies in time-dependent quantum dynamics. The presentation of the paper focuses on the development of accurate or numerically exact time-dependent methods and their specific applications to tetraatomic reactions. After summarizing the current state-of-the-art time-dependent wavepacket approach, a perspective on future (development is provided. 

The reactions H + H2 and F + H2 (and their isotopic variants) have been the benchmark systems in the field of chemical reaction dynamics. For them, fully converged three-dimensional (3D) quantum scattering calculations of state-to-state differential cross sections (DCS) have been performed and accurate comparisons with very detailed experimental observables carried out [3-9]. To date, only for one other neutral three-atom system have the exact (i.e., fully converged) 3D quantum scattering calculations of state-to-state DCS on a reliable ab initio potential energy surface (PES) been carried out, namely, for the prototypical reaction Cl + H2 [10], a system chemical kineticists have been interested in since the time of Max Bodenstein (for a historical overview, see the paper by Truhlar in this volume). However, in contrast to H + H2 and F + H2, no experimental dynamical information is available on Cl + H2. Here we highlight the results of the first dynamical investigation of the Cl + H2 and Cl + D2 reactions by the crossed molecular beam... 

The present Lecture Notes contain the Proceedings of the 1999 Mariapfarr workshop in Theoretical Chemistry. These annual winter workshops, which draw their name from their traditional home , a pleasant resort in the Austrian Alps, are organized by the Computational Chemistry Section of the Austrian Chemical Society. The 1999 event, dedicated to Reaction Dynamics , presented an overview of computational methods developed for the calculation of quantum reaction cross sections and reaction rates. 

In this brief overview no attempt is made to survey the vast amount of literature pertaining to the intramolecular and unimolecular dynamics of highly excited molecules. Instead a discussion is given of recent developments and how they effect our understanding of unimolecular reactions. This overview is primarily limited to unimolecular reactions in the ground electronic state. However, when appropriate, reference is made to the intramolecular and unimolecular dynamics of excited electronic states. For comprehensive discussions of unimolecular reactions readers are referred to the recent articles by Rice, Hase, Quack and Troe, McDonald, Chesnavich and Bowers, Oref and Rabinovitch, and Holmes and Setser, and the books by Robinson and Holbrook, and Forst. ... 

In the sections below a brief overview of static solvent influences is given in A3.6.2, while in A3.6.3 the focus is on the effect of transport phenomena on reaction rates, i.e. diflfiision control and the influence of friction on intramolecular motion. In A3.6.4 some special topics are addressed that involve the superposition of static and transport contributions as well as some aspects of dynamic solvent effects that seem relevant to understanding the solvent influence on reaction rate coefficients observed in homologous solvent series and compressed solution. More comprehensive accounts of dynamics of condensed-phase reactions can be found in chapter A3.8. chapter A3.13. chapter B3.3. chapter C3.1. chapter C3.2 and chapter C3.5. 

The simple pore structure shown in Figure 2.69 allows the use of some simplified models for mass transfer in the porous medium coupled with chemical reaction kinetics. An overview of corresponding modeling approaches is given in [194]. The reaction-diffusion dynamics inside a pore can be approximated by a one-dimensional equation... 

An overview of the time-dependent wavepacket propagation approach for four-atom reactions together with the construction of ab initio potential energy surfaces sufficiently accurate for quantum dynamics calculations has been presented. Today, we are able to perform the full-dimensional (six degrees-of-freedom) quantum dynamics calculations for four-atom reactions. With the most accurate YZCL2 surface for the benchmark four-atom reaction H2 + OH <-> H+H2O and its isotopic analogs, we were able to show the following ... 

The I2 system has been investigated experimentally, theoretically, and computationally by several groups, as a prototype for the study of dissociation and recombination dynamics influenced by the interactions with a surrounding solvent or cluster of solvent molecules[9],[36]-[41]. The system can be effectively modelled by two VB states[9],[41], which allows a focus on several key aspects of the implementation of the theory, without being hindered by the complexity of a multistate calculation. The implementation steps are conveniently collected in the flow chart in Table 1, to which the reader is referred to for a comprehensive overview of our strategy. All the details of the calculation are reported in BH-II. The effective wave function for the I2 reaction system can be written as... 

In this article we have tried to present a general, although somewhat limited overview of molecular dynamics simulations of gas-surface reactions as they pertain to technologically important processes. In the course of this review we have undoubtedly left out a great deal of very important work. We hope. 

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