Linewidth-lifetime correlations with

Although there are only 22 cases listed In Table I, the variety Is great enough to permit several questions to be answered with regard to the correlation of the linewidth-derlved lifetime of the initial state with various structural and dynamical features. First, it Is Important to observe that the total range of lifetimes for these systems Is remarkably small — about 0.4 to 4 ps for molecule-molecule systems and 1.8 to 11 ps for atom-molecule systems. With this In mind, let us examine several parameters which one might expect to be correlated with the lifetime. 

As with Ti relaxation, T2 relaxation has a strong dependence upon the molecular correlation time. Unlike U relaxation, T2 relaxation does not reach a minimum and then increase, but continues to decrease, as shown in Fig. 3. Therefore large, slowly tumbling molecules have very short T2 times. This poses a great challenge in the study of large molecules or molecules in the solid state since the lifetime of the signal is very short and the linewidths are very broad. 

Figure 13. Stochastic simulation of the fluorescence intensity (top) and frequency (middle) correlation functions for a model of spectral diffusion in a glass. The molecule is coupled to a three dimensional distribution of tunneling systems with distributed microscopic parameters. The bottom panel shows the timescale (horizontal) and amplitude of the frequency jumps (relative to the lifetime limited linewidth, vertical scale). The inset in the top panel shows the line-shape and the lifetime limited linewidth as a small bar (from Ref. 77).

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