Vibrational Raman effect, classical theory

In the simple classical theory of the vibrational Raman effect [1] the electric vector is taken as the real expression... 

Raman effect (continued) spectral activity, 339-341 terminology of, 295 vibrational wavefunctione, 339-341 Raman lines, 296 weak, 327-330 Raman scattering, 296 classical theory, 297-299 quantum mechanical theory, 296, 297 Raman shift, 296... 

Placzek s theory (1934) which treats molecules as quantum objects and electromagnetic fields classically, satisfactorily describes the Raman effect on the condition that the exciting frequency differs considerably from the frequencies of electronic as well as of vibrational transitions. 

Fig. 1.32. Classical theory for the origin of the Raman effect. In (a) we see a diatomic molecule where represents protons and represents the center of gravity of the electrons. The electrons are displaced by the external field of the photon and an induced dipole moment is generated which changes when the bond length changes during the molecular vibration. The induced dipole moment is plotted in (b) as an amplitude modulated wave with steady amplitude components shown in (c) from which scattered radiation is generated.

Following the classical approach of vibrational dynamics (as in the case of o--bonded polymers) [67], the experimental data from the oligomers could in principle be used to obtain the phonon dispersion curves of the ideally infinite polymer. In the case of 7r-bonded systems, complications arise because the skeletal modes are strongly CL-dependent and cannot be treated in the standard way. The rationalization of the behavior of the totally symmetric Raman-active normal modes leads to the definition of a CL-dependent intramolecular potential on which the effective conjugation coordinate (ECO theory is based (see Section IV). 

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