Quantum physics microscopic techniques

No attempt will be made here to extend our results beyond the simple lowest-order limiting laws the often ad hoc modifications of these laws to higher concentrations are discussed in many excellent books,8 11 14 but we shall not try to justify them here. As a matter of fact, for equilibrium as well as for nonequilibrium properties, the rigorous extension of the microscopic calculation beyond the first term seems outside the present power of statistical mechanics, because of the rather formidable mathematical difficulties which arise. The main interests of a microscopic theory lie both in the justification qf the assumptions which are involved in the phenomenological approach and in the possibility of extending the mathematical techniques to other problems where a microscopic approach seems necessary in the particular case of the limiting laws, obvious extensions are in the direction of other transport coefficients of electrolytes (viscosity, thermal conductivity, questions involving polyelectrolytes) and of plasma physics, as well as of quantum phenomena where similar effects may be expected (conductivity of metals and semi-... 

Besides its practical importance, photodissociation — especially of small polyatomic molecules — provides an ideal opportunity for the study of molecular dynamics on a detailed state-to-state level. We associate with molecular dynamics processes such as energy transfer between the various molecular modes, the breaking of chemical bonds and the creation of new ones, transitions between different electronic states etc. One goal of modern physical chemistry is the microscopical understanding of molecular reactivity beyond purely kinetic descriptions (Levine and Bernstein 1987). Because the initial conditions can be well defined (absorption of a single monochromatic photon, preparation of the parent molecule in selected quantum states), photodissociation is ideally suited to address questions which are unprecedented in chemistry. The last decade has witnessed an explosion of new experimental techniques which nowadays makes it possible to tackle questions which before were beyond any practical realization (Ashfold and Baggott 1987). 

Physical chemistry lies at the interface of physics and chemistry (hence its name) and deals with the principles of chemistry which, as we have seen, consist largely of quantum mechanics for explaining the structures of atoms and molecules and thermodynamics for assessing the role and deployment of energy. It is also concerned with the rates at which reactions take place, both at the macroscopic level and the microscopic. In the latter it seeks to follow the intimate lives of individual molecules as they are ripped apart and then reconstituted as different substances in reactions. A major activity of physical chemistry is its contribution to the interpretation of investigative techniques, particularly spectroscopy . 

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