Isolated narrow resonance

The formal scattering theory for describing cosipound-state resonances such as the vibrationally predissociaCing states of interest here, is well established (see, e.g., (32-33) and references therein). For an isolated narrow resonance associated with closed channel m, the S-matrix element between (open) channels j and j is given by (33)... 

Figure 4 The phase shift < (E)/tt obtained from the data shown in Fig. 3 using Eq. (55). The sudden unit rise at the energy E = 1994.47 cm"1 is due to the existence of an isolated narrow resonance.

Both in elastic scattering and in reactions, one can find examples where a strong isolated narrow resonance appears in the cross section as a function of energy. Although the first... 

Figure 6. The ID potential in x direction, V x y = 0), when VJ, = 1. The Bound and isolated narrow resonance complex-scaled wavefunctions (real part) are plotted for e = 0.13.

Two line narrowing techniques, matrix isolation and resonant laser excitation, are being used separately and in combination to eliminate inhomogeneous broadening (94). Microenvironmental inhomogeneities are reduced by freezing the sample into uniform site locations in isolation or Shpol skii matrices (95). Alternatively, with highly monochromatic and tunable lasers, it is possible to photoexcite only the subset of emitter sites in a low temperature matrix which have... 

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... 

The basic methods of the identification and study of matrix-isolated intermediates are infrared (IR), ultraviolet-visible (UV-vis), Raman and electron spin resonance (esr) spectroscopy. The most widely used is IR spectroscopy, which has some significant advantages. One of them is its high information content, and the other lies in the absence of overlapping bands in matrix IR spectra because the peaks are very narrow (about 1 cm ), due to the low temperature and the absence of rotation and interaction between molecules in the matrix. This fact allows the identification of practically all the compounds present, even in multicomponent reaetion mixtures, and the determination of vibrational frequencies of molecules with high accuracy (up to 0.01 cm when Fourier transform infrared spectrometers are used). 

The line shapes for the vibrational levels, and specifically that of v = 20 of the excited surface 1 are much narrower than the energy level spacing therefore, all the resonances are isolated as in the atomic case discussed above. The decay curves resulting from coupling the a) = v = 20) with the b) = v = 30) are shown in Figure 9.13. Again the method is very successful in completely suppressing the decay. 

It is hardly surprising that, as the microwave power is raised, higher order multiphoton processes are observed. On the other hand, it may be surprising that for each m 0 the cross sections first increase then decrease with microwave power. For example, the m = cross section is clearly zero in the lowest trace. Similarly, the m = 0 cross section vanishes in the trace one above the lowest but reappears in the lowest trace. Such behavior, typical of the strong field regime, is not predicted by perturbation theory. Close inspection of Fig. 15.5 reveals that the positions of the collisional resonances shift to lower static field as the microwave power is raised. Finally, in contrast to the usual observation of broadening with increased power, the (0,0)m resonances, which are well isolated from other resonances, develop from broad asymmetric resonances to narrow symmetric ones as the microwave power is raised. 

Conversely, a coherent superposition of continuum states with a population closely reproducing an isolated peak in the density of states, which corresponds to a resonance, can be built in such a way to give rise to a localized state. From this localized state, there will be an outward probability density flux, i.e., it will have a finite lifetime. In the limit of a resonance position far from any ionization threshold and a narrow energy width, the decay rate will be exponential with the rate constant T/ft. The decay is to all the available open channels, in proportion to their partial widths. 

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