Weak resonance

SYMMETRY BREAKING IN CASE OF WEAK RESONANCE BETWEEN POLARIZED FORMS... 

Another interesting problem coneems the case of a weak resonance between two ionic VB structures as occurs in the singlet nn state of ethylene (and longer polyenes). This state (the allowed By state) is of ionic VB content... 

CAS F calculations are not a universal solution to symmetry-breaking of the wave functions, and for such weak resonance problems it is far more reliable to start from state average solutions which treat on an equal footing the two configurations which interact weakly. 

Re-evaluation of pulse delay times used to record fullerene 13C NMR spectra revealed that a 16 s pulse delay, twice the value for a standard detection, allowed the observation of a weak resonance in the sp3 region at 90.4 ppm in the 13C NMR spectrum of the unlabeled heterofullerene 114. Attempts were made to optimize the NMR experimental parameters for a long 7 i, i.e. the variation of delay times and pulse angles. Various conditions were tried on the labeled material without success. This is probably due to the mixture of the labeled and unlabeled 114 which give too low S/N for signal detection. Table 49 summarizes the NMR results obtained and illustrates a distinct pattern of the azafullerenes. 

FIGURE 9.12 (a) Calculated FE-CARS radiation profile when a HGOl excitation field overlaps with a lateral interface between a resonant and a nonresonant material. Note that the intensity along the optical axis is no longer zero due to partial lifting of the phase step by the interface. The inset shows the excitation field relative to the orientation of the interface, (b) Comparison of the calculated spectral dependence of CARS in a bulk material with a weak resonance and FE-CARS measured at an interface similar to the one considered in (a). Note the Raman-like spectral dependence of the FE-CARS signal. 

P6 9-10 2p(ris subband) non-observed surface observed for non composition cleaved or Ar-effect sputtered single crystals nonobserved for in situ scraped single crystals 2p(6d) very weak resonance character behaviour, i.e. no 5 f ofv.b, character... 

Starting from a crack that is small compared with a wavelength, the effect on V z) when the lens is directly over the crack initially increases with crack depth. The chief information about the crack depth lies in the phase there is a weak resonance when the crack depth is comparable with the Rayleigh wavelength, and beyond that the contrast tends to become independent of the crack... 

NMR is a widely used and important technique for molecular structure determination as applied to bulk materials, where it competes, often advantageously, with vibrational spectroscopy. However, a lack of sensitivity has limited its application to the study of adsorption on high-area finely divided surfaces. Also, certain metals with bulk magnetic properties—e.g., Fe, Co, and Ni (but not the other group Vlll transition metals)—cannot be studied by the technique as their magnetism causes very broad and weak resonances from adsorbed species. 

In condensed-phase CARS, the effects of the nonresonant susceptibility x(3)nr are most profound when a sample with weak Raman modes is embedded in a nonlinear medium. The nonresonant background of the latter can be easily comparable to or larger than the resonant contribution from the sample of interest. This is a situation commonly encountered in biological applications of CARS microscopy. Depending on the experimental situation, the CARS detection sensitivity to weak resonances can then be restricted either by the nonresonant background or by the photon shot-noise [62]. To maximize either the relative or the absolute CARS intensity, nonresonant background suppression schemes [44, 60, 61, 63, 64] and optical heterodyne detection (OHD) techniques [65-67] have been developed during recent years. 

The weak resonance observed in the range 14-15 ppm can be assigned to the methyl groups of the ends in the main chain. This resonance, however, is not pertinent to our present analysis. 

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