Remarks on quantum reactive scattering

The detailed study of the dynamics of simple chemical reactions in the gas phase and on solid surfaces is a major area of modern physical chemistry. Experimental progress in this field has developed to such an extent that it is possible to get a complete picture of the state-to-state dynamics of atom-diatom reactions such as 

Up to 1986, accurate quantum mechanical calculations had then only been performed on the simplest 3D chemical reactions 

The most detailed quantity that can be measured in a reaction dynamics experiment is the state-to-state differential cross section [18] 

The theoretical methods reviewed in the next chapters produce all of these quantities, ranging from state and energy selected differential cross sections to temperature dependent rate coefficients. Thus the theory of chemical reaction dynamics provides a crucial link between the results obtained in detailed state selective molecular beam experiments and thermally averaged bulb measurements. 

One might wonder since classical trajectory calculations on quite complicated reactions have been performed for some time [20], why the coordinate problem described above really is so obtrusive in the quantum mechanical case. The reason for this is simply that quantum mechanical calculations must, by virtue of the Uncertainty Principle describe all regions of the available coordinate space at once. Classical trajectory calculations effectively access only a single point in this space at a time, which by comparison is a great deal easier to arrange. In fact the coordinate problem encumbers clas- 

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