Molecular liquid state rotation-translation coupling

In Section IV the computer simulation is extended to describe the effects of excitation in chiral molecules and racemic mixtures of enantiomers. The modification of the dynamical properties brought about by mixing two enantiomers in equimolar proportion may be explained in terms of rotation-translation coupling. The application of an external field in this context ai iplifies the difference between the field-on acf s and cross-correlation of enantiomer and racemic mixture and provides a method of studying experimentally the fundamental phenomenon of rotation-translation coupling in the molecular liquid state of matter. 

Relative to solids, it is the increased molecular motion, particularly translational and rotational, that provides the dominant relaxational pathways in liquids. Whereas the detailed molecular structures of solids are relatively easy to characterize, it is far more difficult to do this for liquids. Consequently, in the latter case it is convenient to leave the phonon and quantum mechanical approach behind and revert to a classical description of the system. For such a description of a liquid system the constituent species can be considered to generate positionally dependent and randomly fluctuating electric and magnetic field within the sample. It can then be seen that it is possible for the magnetic field to have a component, at a particular nucleus, which varies with the same frequency and sense as the Larmor frequency of the nucleus. Thus if the nucleus is in an excited state, its coupling to the rest of... 

In liquids and dense gases where collisions, intramolecular molecular motions and energy relaxation occur on the picosecond timescales, spectroscopic lineshape studies in the frequency domain were for a long time the principle source of dynamical information on the equilibrium state of manybody systems. These interpretations were based on the scattering of incident radiation as a consequence of molecular motion such as vibration, rotation and translation. Spectroscopic lineshape analyses were intepreted through arguments based on the fluctuation-dissipation theorem and linear response theory (9,10). In generating details of the dynamics of molecules, this approach relies on FT techniques, but the statistical physics depends on the fact that the radiation probe is only weakly coupled to the system. If the pertubation does not disturb the system from its equilibrium properties, then linear response theory allows one to evaluate the response in terms of the time correlation functions (TCF) of the equilibrium state. Since each spectroscopic technique probes the expectation value... 

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