Inhomogeneous bands

Homogeneous and inhomogeneous band broadening. Red-edge effects... 

Note that the same concept could be used differently If molecules that are excited by the first light beam fluoresce, we would expect the fluorescence spectrum observed following such excitation to be considerably narrower than what would be nonnally observed after exciting the full inhomogeneous band. 

The protein shows a markedly different behavior (Fig. 16). The color effect in the shift with pressure varies in a nonlinear fashion over the inhomogeneous band. In the red and blue edge, we measure a linear behavior, yet the corresponding slopes differ by a factor of almost 3. Because we associated the slope with the compressibility, we have to conclude that the compressibility of the protein varies within a factor of 3. 

Because a pressure change on the order of 1 MPa induced a shift on the order of 0.1 cm , we need something like 1 GPa to induce a shift on the order of the inhomogeneous band. Hence, kAp = 0.1 and we have... 

Fig. 7.15 Transition from homogeneous to inhomogeneous (banded) deformation behavior of Pd8oSi2o on the temperature-strain-rate plane (from Megusar et al. (1979) courtesy of Elsevier).

The advantage of a hole burning experiment is that the change in line width under pressure can be measured much more accurately than the inhomogeneous bands. No correc-... 

First of all, we need to discuss main ideas concerning homogeneous and inhomogeneous band broadening in solids and to explain the terminology which will be used in this review. 

Suppose the dye probe molecule is photoreactive. Then, to understand the essential features of hole burning, it suffices to consider three states only the ground state Sq, the first excited singlet state Si, and the photoproduct state Pq (Figure 3). For simplicity we assume that Pq has an infinite lifetime. The absorption spectrum of Pq is shifted as compared to that of Sq because Pq represents a structurally different molecule. Consider Figure 4 narrow-bandwidth laser light is tuned to some position within the inhomogeneous band. We denote the respective frequency by Vl. Excitation leads to photochemistry hence, population is transferred to Pq and, concomitantly, Sq... 

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