Photoexcitation spectral distribution

The copper system appears to behave similarly to the silver system, and it may be used here in order to illustrate the idea of "selective, naked-cluster cryophotochemistry 150,151). A typical series of optical-spectral traces that illustrate these effects for Cu atoms is given in Fig. 15, which shows the absorptions of isolated Cu atoms in the presence of small proportions of Cu2, and traces of Cus molecules. Under these concentration conditions, the outcome of 300-nm, narrow-band photoexcitation of atomic Cu is photoaggregation up to the Cus stage. The growth-decay behavior of the various cluster-absorptions allows unequivocal pinpointing of UV-visible, electronic transitions associated with Cuj and Cus 150). With the distribution of Cui,2,3 shown in Fig. 15, 370-nm, narrow-band excitation of Cu2 can be considered. Immediately apparent from these optical spectra is the growth (—10%) of the Cu atomic-resonance lines. Noticeable also is the concomitant... 

If microstates lead to the existence of a distribution of energies of interaction between aromatic groups and neighboring groups of atoms, then the individual spectra of these groups in different microstates shift differently, which results in an inhomogeneous contour of the absorption band. The application of selective photoexcitation permits specific effects of the distribution of microstates on spectral, temporal, and polarization fluorescence properties to be observed. 221 Such effects have been observed in studies of proteins, 1,8) and, as we show below, they may be used to obtain important information on dynamics. 

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