Light polarized visible

Aa is the absorbance in the tilted geometry, Az the absorbance measured in normal incidence geometry with light polarized along the Z-axis, and n the refractive index of the sample. The isotropic refractive index in the visible range is often used as a first approximation, but quantitative measurements require knowledge of the anisotropic refractive indices at the wavelength of interest [29]. 

Figure 10.1 Comparisons of visible to near-infrared spectra of calcic pyroxene in transmitted and reflected light. Polarized absorption spectra of single crystals are correlated with the reflectance spectrum of a powdered sample of the same mineral (cf. fig. 5.14).

A. The fibers, although large enough to react with polarized light, are visible but have no brightness or color of their own. The color matches the red color of the background. 

Fig. 22(b) shows polarized visible absorption spectra of mixed LB films of MS-C2o binary and MS-C20-AL18 ternary systems prepared by using an aqueous subphase containing Cd2+ ions, where the ratio in the mixed system is [MS] [C20] [AL18] = l 2 x (x — 0 and 1) [77-84]. The thick and thin lines in Fig. 22(b) refer to the spectra, Atl and A , measured by linearly polarized light with the electric vector parallel and perpendicular to the dipping direction of the substrate, respectively. For x = 0, a sharp absorption peak is observed at 590 nm, which is red-shifted from the MS monomer peak at around 540 nm. The dichroic ratio R of the 590 nm band is R> 1, where R is defined as A /A . For x= 1.0, on the other hand, a sharp blue-shifted band with R< 1 appears at 505 nm. Fig. 22(c) refers to the cases of the corresponding binary and ternary systems fabricated under the subphase without the Cd2+ ions [84], Unlike the results in Fig. 22(b), remarkably red- and blue-shifted bands are not observed... 

Fig. 22. (a) Chemical structure of MS and a schematic representation of the intramolecular charge transfer in MS. Polarized visible absorption spectra of the mixed LB films of the MS-C20 binary and MS C2o AL X ternary systems with the molar mixing ratios of [MS] [C20] [ALi8] = 2 x (x = 0 and 1) fabricated under a subphase (b) with and (c) without Cd2+ ions. The thick and thin lines represent An and A measured by linearly polarized light with the electric vector parallel and perpendicular to the dipping direction of substrates, respectively. (Reproduced with permission from Ref. [84]. Copyright (2006) Elsevier.)... 

Figure 1 Myoglobin and the heme-CO coordinate system 6 is the angle between C-0 and the heme plane normal and

Fig. 13.1. Thin section micrograph in cross-polarized visible light of two feldspar grains in the upper cm of the mineral soil of a podzol formed in a 5400-year-old dune in northern Michigan. The left grain shows signs of chemical weathering, the right grain is turmelled.

Figure 2. Reflection spectrum of poly TS crystal at room temperature for light polarized parallel to the polymer chains (a) detail of the reflection in the visible and (b) spectrum over the range 1.6 to 12 eV f38J.

The mechanism of the photochemical reaction has been the subject of some elegant experiments involving polarized light both for photolysis and for spectroscopic measurements. Unpolarized UV photolysis of Cr(CO)6 in pure methane matrices yields randomly oriented Cr(CO)s- CH4 molecules. Polarized visible photolysis leads to specifically oriented Cr(CO)s- CH4 molecules, as evidenced by the development of linear dichroism in the visible absorption band. The direction of the spectral dichroism depends upon the direction of polarization of the irradiating beam (equation 22). 

Light (uv-visible-near-ir radiation) reflected back from a flat, highly polished surface of a solid measured in intensity as a function of varying wavelength. Measurements can be made using plane-polarized light, at normal incidence, and on oriented faces of single crystals... 

Taking into account the fact that the absorption spectrum in light polarized parallel to planar groups contains only a very weak absorption band in the visible range, it must be concluded that all the new intense bands of the crystalline state have a characteristic polarization perpendicular to the planes which produces the dichroism. 

Animal GDH s are unusual proteins in that they dextrorotate plane-polarized visible light (137) the positive rotations do not result from polymerization (144)- In contrast, the NADP-GDH from bakers yeast is levorotatory (69). The reported lack of reproducibility of rotations recorded in the ultraviolet, which may have been caused by denaturation at low ionic strength, can be prevented by including glycerol in the solution (105). Parameters calculated by the procedmes of Moffitt (143), and of Shechter and Blout (143), and recorded in Table IV indicate a high a-helix content. 

Fig. 14. Optical absorption spectra of all-/ra/w- carotene single crystals in the visible to mid-infrared region recorded at room temperature by irradiating light polarized along a ox b crystal axis.

The optical reflectance of crystalline films of ( SJVjx from the near uv through the visible region is metal-like in character for light polarized parallel to the polymer chain axis. The covalent polymer has the optical and electrical properties of a low-dimensional metal. 

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