Residual absorption

In a crystalline medium, the parametric gain (2) T2 is propor-tionnal to d2 Ip n-3 and the oscillation condition r2A2>aA where a is the signal residual absorption (dramatically increased by any crystalline defect), d the efficient phase-matched nonlinear susceptibility, n an average refractive index, Ip the pump intensity (limited by the optical damage threshold) and A the effective interaction length (also limited by any source of crystalline disorientation). 

The achievement of the corresponding monocrystals of sufficient optical and crystalline quality is made possible only after very thorough purification. Chemical impurities are known to disturb the crystal lattice through the occurence of twins, veils dislocations, rounding-off of faces ultimately quenching further growth. Any crystalline defect dramatically increases the residual absorption coefficient and lowers the optical damage threshold. 

Due to the generally low concentration of contaminants, an important parameter for QC labs is the limit of detection. For rhuMAbHER2 this limit was estimated to be 2 ppm. Care should be exercised when analyzing low-concentration samples because ampholytes may show residual absorption even at 280 nm.86 This problem can be reduced by decreasing the ampholyte concentration to 0.5% w/v. 

Diphenolmethane derivatives (p. 177) were developed from phenolphthalein, an accidentally discovered laxative, use of which had been noted to result in rare but severe allergic reactions. Bisac-odyl and sodium picosulfate are converted by gut bacteria into the active colon-irritant principle. Given by the enteral route, bisacodyl is subject to hydrolysis of acetyl residues, absorption, conjugation in liver to glucuronic acid (or also to sulfate, p. 38), and biliary secretion into the duodenum. Oral administration is followed after approx. 6 to 8 h by discharge of soft formed stooL When given by suppository, bisacodyl produces its effect within 1 h. 

Plotted curves illustrating this relation, Fig. 5, resemble very much the curves of Fig. 3. Consequently, one cannot infer from a measured intensity or energy saturation curve reliable values of molecular data without additional information, as for instance an independent measurement of ksr Another possibility is a measurement of the temporal characteristics of the bleaching as demonstrated in an experiment by Hercher et al. 14>. These authors bleached a thoroughly degassed solution of metal-free phthalocyanine in 1-chloronaphthalene by a ruby laser pulse (694.3 nm) of about 59 nsec pulse width. At the same time they measured the absorption at 632.8 nm using a He-Ne-laser, and the result of this measurement is shown in Fig. 6. It clearly demonstrates that the sample was almost completely bleached even before the laser pulse reached its maximum intensity, and that almost all of the molecules were stored in the triplet state because the transmission did not decrease with the fall of the laser intensity for at least 100 nsec. A small residual absorption indicates triplet-triplet absorption. 

There are many dyes which fulfill the above requirements, few of which have been used until now. The first dyes used with a ruby laser were phthalocyanines the free base as well as chloro-aluminum- and vanadium-phthalocyanine in 1-chloronaphthalene or nitrobenzene 22>. While these dyes show little residual absorption 14> and good photochemical stability, the solubility is relatively low and the solvents are not well suited to operation in a laser resonator. 

A recent study of the hydrogenation of propyne on Pd/Zr02 showed residual absorptions from surface species after evacuation. These were attributed to di-cr and propylidyne adsorbed species, but no spectra were illustrated (113). SER spectra of the alkynes but-2-yne, pent-l-yne, and pent-2-yne on a gold electrode have been measured (83). At -0.4 V the nC=C modes are lowered by about 110 cm 1 from the values for the free alkynes. For the alk-2-ynes the shift increases by a further 10 cm"1 upon a change of the potential to +0.4 V. The spectrum of but-2-yne has two principal component bands, at 2134 and 2109 cm-1 in the pC=C region, and also shows a downward shift for the nCH3 modes. 

In distilled water and tap water without chlorine it is possible to measure the liquid ozone concentration and the unsaturated organic substances by using Na2S203. The first absorption value at X = 254 nm represents the sum of the organic substances and the liquid ozone concentration. After destroying the ozone the residual absorption is correlated to the organic matter (Tsugura et al., 1998). 

Now, the problem is how could we separate the contribution by the CO absorption layer from the stronger photospheric component. For this purpose, we compared the observed profiles with predicted ones based on model atmospheres and found appreciable residual absorption for low excitation lines while no residual for high excitation lines. Then, the contribution by the CO absorption layer has been separated by subtracting the photospheric contribution from the observed profile,in low excitation CO lines. A detailed analysis on separated excess CO absorption gives the results as follow( as for detail, see Tsuji,1987b) ... 

The intermediate(s) responsible for the residual absorption a3 could either be additional primary photoproduct(s) or secondary produces), such as Ij, which have already been formed but are further transformed much more slowly [121, 123] than the I700 and I700 species possessing microsecond lifetimes. A more accurate evaluation of the data was not possible since very low absorbances had to be monitored and the decay time of a3 was beyond the nano- to millisecond resolution of the experimental set-up used [113]. 

Upper curve (a)—Residual absorption, measured 400 ysec after flash—... 

Somewhat related to the (cationic) cyanines are the squarylium dyes which are overall charge neutral species derived from squaric acid. They are easily prepared, have high molar absorptivities (>100,000), but typically are unstable to hydrolysis in dipolar aprotic solvents. They are characterized by a sharp strong absorption which lies at wavelengths longer than 640 nm, with no other identifiable electronic transitions in the visible (Figure 2). The vibronic structure of these dyes may show only one shoulder corresponding to a reasonable value for a C-C or C-0 stretch. We were able to systematically vary the structure of a series of squarylium dyes in order to test assumptions about the structure-property relationship for minimization of the residual absorption. 

Based on the expression for, a large increase in the useful NLO coefficient for a fixed wavelength is predicted in the case where the absorbance of the NLO dye lies between the fundamental and second harmonic. Residual absorption at the second harmonic is the limiting factor in the practical application of this technique, and has been addressed through the synthesis of new dyes. Improvement of lOx in reducing this absorbance has been achieved, and another factor of 5-lOx is estimated to be required before practical devices can be fabricated. Franck-Condon effects (vibronic structure) appear to be responsible for this residual absorption because small, rigid chromophores are often correlated with the lowest amounts of absorption. Chromophores based loosely on... 

Figure 10.6. Remote-sensed spectra of representative areas on the Moon s surface (from Gaddis et al., 1985). Left telescopic spectral reflectance scaled to unity at 1.02 i.m and offset relative to adjacent spectra right residual absorption features for the same measurements after a straight line continuum extending from 0.73 pm to 1.6 pm has been removed, (a) Highland soil sampled at the Apollo 16 landing site (b) high-Ti mare basalt at the Apollo 17 landing site (c) low-Ti mare basalt at Mare Serenitatis and (d) pyroclastic deposits at Taurus-Littrow.

Figure 10.9 Reflectance spectra obtained from Earth-based telescopes for small (< 5 km diameter) areas within the Copernicus crater on the Moon (from Pieters et al., 1985). Left reflectance scaled to unity at 1.02 im right residual absorption after continuum removal. Spectra are offset vertically, (a) Wall and (b) floor areas containing orthopyroxene are deduced to be of noritic composition (c) floor containing pyroxene and glass is an area of extensive impact melt and (d) central peak containing olivine is deduced to be troctolite.

Figure 6 UV-Vis spectral changes upon 313- and 366-nm irradiation of glassy nematic films of HMW1. (a) Before irradiation, (b) After irradiation. Residual absorption at ca. 280 nm is attributed to cyclobutane photoproducts. Residual absorption beyond ca. 340 nm is mostly due to photo-Fries rearrangement products. (Reprinted with permission from Creed et al. [23]. Copyright 1990 American Chemical Society.)...

A trial was made to take a look at the valence of iron in adrenodoxin (29) using 3 moles of p-chloromercuribenzoate (PCMB) per gram atom of iron (less than saturated level of PCMB), all of the iron could be extracted by 5% trichloroacetic acid solution as ferric iron, which produces a ferrous-o-phenanthroline complex only by the addition of ascorbate as reductant. In the absence of the mercurial, some 50% or more of the iron atoms in the protein can be removed in the ferrous state. This result indicates that the acid extraction causes intramolecular reduction of the protein-bound iron. As shown in Fig. 10, 5.7 M urea as a protein denaturant can slowly bleach the visible absorption under aerobic conditions. About 10% of the residual absorption remains at 414 mp after the reaction is completed. In the presence of both urea and o-phenanthroline, all of the iron present in adrenodoxin reacts with o-phenanthroline to produce the ferrous complex under aerobic conditions. Similar experiments under anaerobic conditions reveal that the... 

Figure 16 Photothermal deflection spectrum of a NH3 -compensated trans-VA. Dots and dashed line show the absorption edge recorded on two films, 4 p.m and 0.1 xm, respectively. Dotted line shows the residual absorption of an uncompensated sample. Solid line sketches the expected neutral soliton absorption in the absence of electron correlation. (From Ref. 130.)...

The application of an electric field between the electrodes results in a realignment of the nematic liquid crystal mixture and the dichroic dye molecules parallel to the electric field resulting in a lower optical density (absorption) and, theoretically, the disappearance of colour assuming an ideal order parameter (S = 1) of the nematic liquid crystal director and the dye molecules. A residual absorption in this state gives rise to a display with a strongly coloured background and weakly coloured information. 

An additional factor to be considered in computing a calculated absorptivity is that Xmax varies from one protein to another, and we do not have complete tables of residue absorptivities at frequent wavelength intervals. Therefore we approximate the residue absorptivity at the wavelength of the protein peak. A common approximation, as in the ribonuclease example above, is simply to use the value of e at Xmax for the model compound and hope that it will not be too poor an approximation. 

Metallic polymers have a lower density of electrons both the length of the repeat unit along the chain and the interchain spacing are relatively large compared to the interatomic distances in conventional metals. Typically, for metallic polymers N is of the order 5 x 10 cm . Thus, for metallic polymers, the plasma frequency is at approximately 1 eV [66,67]. The reflectance of high quality, metallic polypyrrole (doped with PF ) is shown in Fig. III-2. Metallic polymers exhibit high reflectance (and thus look shiny ) in the infrared, but they are semitransparent in the visible part of the spectrum. The residual absorption... 

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