Relaxation transitions background

The optical properties of organic conductors may be described by the simplest model, which assumes noninteracting electrons (one-electron model). In this approximation the infrared (IR) properties may be derived in the self-consistent field approximation. Assuming a frequency-independent relaxation rate, y, and a background dielectric constant arising from virtual high-frequency transitions, e0, the result takes the Drude form [12] ... 

Many workers have in fact used density matrix methods for the calculation of line shapes and intensities in multiple resonance experiments, and two excellent reviews of the background theory are available. (49, 50) In addition there is also a simple guide (51) to the actual use of the method which is capable of predicting the results of quite elaborate experiments. Major applications have included the calculation of the complete double resonance spectrum from an AX spin system which gives 12 transitions in all (52) an extremely detailed study of the relaxation behaviour of the AX2 systems provided by 1,1,2-trichloroethane and 2,2-dichloroethanol (53) the effects of gating and of selective and non-selective pulses on AB and AX spin systems and the importance of the time evolution of the off-diagonal elements of the density matrix in repetitively pulsed FT NMR and spin-echo work (54) the use of double resonance to sort out relaxation mechanisms and transient responses (55) the calculation of general multiple resonance spectra (56) and triple resonance studies of relaxation in AB and AX spin systems. (57)... 

In the case of T2, the results for incoherent light are entirely the same as those for short pulse except that the T2 decay characteristic in the correlation trace appears symmetrically with respect to x for homogeneously broadened transition. In the case of Tj = T2, however, the appearance of T -dependent background and the modification of relaxation decay due to the Ti effect occur for incoherent light, while the results are independent of for short pulse input. These features complicate the interpretation of the results for incoherent light. But they still serve for the determination of T2, because the decay characteristics are dominantly governed by T2. All these behaviors can well be explained physically by... 

Fig. 39. Background corrected spectra of YbInCu4 showing the different magnetic relaxation behavior above and below the valence phase transition which occurs at 45K. The hatched area on the right-hand side represents the magnetic contribution. (From Severing et al. 1990b.)...

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