Dynamics of collision

As with any collision process, to understand the dynamics of collisions we need an appreciation of the relevant forces and masses. Far from the surface, the incoming atom or molecule will experience tire van der Waals attraction of the fonn... 

Statistical theories, such as those just described, are currently the only practical approach for many ion-neutral reactions because the fine details of the collision process are unknown all the information concerning the dynamics of collision processes is, in principle, contained in the pertinent potential-energy surfaces. Although a number of theoretical groups are engaged in accurate ab initio calculations of potential surfaces (J. J. Kaufman, M. Krauss, R. N. Porter, H. F. Schaefer, I. Shavitt, A. C. Wahl, and others), this is an expensive and tedious task, and various approximate methods are also being applied. Some of these methods are listed in Table VI, for example, the diatomics-in-molecules method (DIM). 

Crossed-molecular-beam studies of differential scattering of metastable noble-gas atoms with ground-state noble-gas atoms or simple molecules is the major topic of this chapter. These studies have been carried out recently at several laboratories with the common goal of finding both real and imaginary parts of the interaction potentials to further our understanding of the dynamics of collision processes involving metastable noble-gas atoms. 

The integrand decreases as an inverse cube of the distance separating the molecule from the charged particle (i.e., as Rq3), meaning that the interaction is important only at distances about the distance of closest approach. Using the classical dynamics of collisions,148 we find the... 

At the same time it is possible to obtain sufficiently interesting information on the dynamics of collisions by means of technically simpler measurements of the polarization of laser-induced fluorescence at excitation of molecules in bulk. A short account of such investigations is given in [288]. 

This chapter concentrates on the experimental determination of product energy distributions and their interpretation in terms of the dynamics of collisions. In a volume concerned with excited states, it seemed appropriate to bias the article in favor of the spectroscopic methods and results, at the expense of the crossed-beam studies. Electronically adiabatic reactions, which pass smoothly from reactants to products in their electronic ground states, are emphasized, since the results of such processes may be compared with trajectories computed with the equations of classical, rather than wave, mechanics, and the effects of kinematic factors on the sharing of energy can be explored. 

Recent advances have resulted from the development of more powerful experimental methods and because the classical collision dynamics can now be calculated fully using high-speed computers. By applying Monte Carlo techniques to the selection of starting conditions for trajectory calculations, a reaction can be simulated with a sample very much smaller than the number of reactive encounters that must necessarily occur in any kinetic experiment, and models for reaction can therefore be tested. The remainder of this introduction is devoted to a simple explanation of the classical dynamics of collisions, a description of the parameters needed to define them, and the relationship between these and the rate coefficient for a reaction [9]. 

Angular momentum enters into the dynamics of collisions in two principal guises. It is created when the initial momentum of relative motion is converted on impact, to orbital AM. This orbital AM is then partitioned between molecular rotation and recoil orbital AM. Molecular rotation plays a key role here since spectroscopic methods allow directly measurement of rotational energy and... 

Mullin A S, Park J, Chou J Z, Flynn G W and Weston R E Jr 1993 Some rotations like it hot selective energy partitioning in the state resolved dynamics of collisions between CO2 and highly vibrationally excited pyrazine Chem. Phys. 175 53-70... 

The high time resolution that is achievable with pulsed or mode-locked lasers (Chap. 6) opens the possibility for studying the dynamics of collision processes and relaxation phenomena. The interesting questions of how and how fast the excitation energy that is selectively pumped into a polyatomic molecule by absorption of laser... 

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