Wavelength cutoff distribution

Figure 14.4. Variation in x-ray distribution with voltage yttrium target). The characteristic Y Ka line is at 0.83 A. The short wavelength cutoff is indicated by an arrow for each voltage. From F. J. Welcher, ed.. 

Table I lists a variety of organic nonlinear materials which have appeared in the literature their relative powder efficiencies, absorption cutoffs and /3 values (if available) are also provided. These materials are "typical" only in that they represent results from the few classes of organic compounds investigated to date, yet they are instructive in that one learns which molecular properties may be important. A few caveats are in order to avoid misinterpretation of the data in Table I. Except for compound 10 (19) all the powder efficiency and cutoff data are from our own measurements. Powder measurements were performed on ungraded samples using the Nd YAG output at 1.06/t as fundamental since powder efficiency is a function of particle size distribution and a variety of other factors (3) these values are only semiquantitative. The cutoff values are the wavelengths for which 10-4M solutions in ethanol (unless otherwise indicated) have no absorbance. The cutoff values will be similar to those found in crystal state except where intermolecular charge transfer is important in the crystal or the molecule is solvatochromic, this latter effect being quite common for cyanine dyes such as...

Minor differences in the spectral distribution found in different kinds of equipment are mainly caused by a variation in filter elements for the infrared part (surface temperature) and the UV cutoff. The radiation level in the UV wavelength range may also vary between instruments. 

The distribution of retardation times is also modified by the presence of the network. Long wavelength modes are damped by the network and the distribution of chain lengths between crosslinks should lead to a softened cutoff at the long relaxation time end. This complexity suggests that actual equilibrium data should be taken for very long times, because full equilibrium may require extensive patience. Even if the network were perfect with identical numbers of monomers between crossUnks and no chain ends or loops, the physical location of the crossUnks would reflect the Gaussian statistics and the response would still be complex. 

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