Polarized optical absorption

The optical transition moments for vibrational or electronic transitions between defect states have specific orientations with respect to the defect coordinates. The absorption strength of polarized light for each of the differently oriented centers is proportional to the square of the component of the transition moment that is along the polarization direction. Hence, a stress-induced redistribution of the defects among their different orientations will be detected as an anisotropy in the polarized optical absorption. A convenient measure of the anisotropy is the dichroic ratio, defined as... 

Measurements of binding curves without influencing the equilibria can be performed if the readout for complex formation is correlated with a change in a macroscopic signal. This can be either a change in fluorescence intensity, fluorescence polarization, optical absorption, or heat of association (see next chapter). Assume an equilibrium... 

Polarized optical absorption measurements have been made for the bis (N,N-diethyldithiocarbamato)silver(II) complex also diluted in the zinc complex.544 Two spin-allowed transitions were observed ZA2— 2B1 (625nm) and 2A2— 2Bz (425 nm). 

Faye, G. H., Manning, P. G. Nickel, E. H. (1968) The polarized optical absorption spectra of tourmaline, cordierite, chloritoid, and vivianite ferrous-ferric electronic interaction as a source of pleochroism. Amer. Mineral., 53, 1174—201. 

Finch, J. Gainsford, A. R. Tennant, W. C. (1982) Polarized optical absorption and 57Fe Mossbauer study of pegmatitic muscovite. Amer. Mineral., 67,59-68. 

Polarized optical absorption studies have been carried out on diphenylmethylene (Gloss et al., 1966a Hutchison, 1967). 

The polarized optical absorption and luminescence spectra of [M(porphine)j (M = Pd, Ni, or Hj) doped in triphenylene host crystals have been reported. Other workers have also reported high-resolution Q-band absorption and emission spectra of [M(porphine)] (M = Pd, Pt, or Cu) in single crystals of n-octane at 4.2 The lifetimes determined from the 0-0 linewidths in the absorption spectra were also given. 

Hashimoto H, Kiyohara D, Kamo Y, Komuta H and Mori Y (1996)Molecularorientationofall-rrani-i3-carotene in spin-coated film and in Langmuir-Blodgett film as detected by polarized optical absorption and reflection spectroscopies. Jpn J Appl Phys35 281-289... 

Filut MA, Rule AC, Bailey SW (1985) Crystal structure refinement of anandite-20i , a barium- and sulfurbearing trioctahedral mica. Am Mineral 70 1298-1308 Finch J (1963) A colorimetric classification of Australian pegmatitic muscovite. Am Mineral 48 525-554 Finch J, Gainsford AR, Tennant WC (1982) Polarized optical absorption and Fe Mossbauer study of pegmatitic muscovite. Am Mineral 67 59-68... 

Polarized optical absorption spectra of the diradical (DR), the asymmetric carbene (AC) and the stable oligomer (SO) molecules. The dimer (n=2) spectra (A,a,ot) are given by the upper part. The spectra with n > 2 are shown in the lower part. 

Ferroelectric materials are capable of being polarized in the presence of an electric field. They may exhibit considerable anomalies in one or more of their physical properties, including piezoelectric and pyroelectric coefficients, dielectric constant, and optoelectronic constant. In the latter case, the transmission of light through the material is affected by the electric field, which produces changes in refractive index and optical absorption coefficient. Varying the applied field changes the phase modulation. 

The optical absorption of the solvated electron, in the continuum and semicontinuum models, is interpreted as a Is—-2p transition. Because of the Franck-Condon principle, the orientational polarization in the 2p state is given... 

Experimental verification of the ISRS generation can be primarily given by the pump polarization dependence. The coherent phonons driven by ISRS (second order process) should follow the symmetry of the Raman tensor, while those mediated by photoexcited carriers should obey the polarization dependence of the optical absorption (first order process). It is possible, however, that both ISRS and carrier-mediated generations contribute to the generation of a single phonon mode. The polarization dependence is then described by the sum of the first- and second-order processes [20-22], as shown in Fig. 2.3. 

It should first be noted that the measurement of emission anisotropy is difficult, and instrumental artefacts such as large cone angles of the incident and/or observation beams, imperfect or misaligned polarizers, re-absorption of fluorescence, optical rotation, birefringence, etc., might be partly responsible for the difference between the fundamental and limiting anisotropies. 

The optical absorption spectra depend on the solvent. They are red-shifted with the decreasing polarity of the solvents as in EDA, liquid NH3, where they appear at a longer wavelength than in water [49], and blue-shifted in methanol [38]. Moreover, the maximum in NH3 is red-shifted with the increase of temperature. In water, the Ag band is almost unchanged in the range 20-200 °C, while that of Ag2 is markedly shifted to the red [50]. Electron spin echo modulation analysis of Ag in ice or methanol glasses has concluded to a charge transfer character to solvent (CTTS) of the absorption band [51]. 

Evidence for the contribution of the CIO + BrO interaction is found in the detection and measurement of OCIO that is formed as a major product of this reaction, reaction (31a). This species has a very characteristic banded absorption structure in the UV and visible regions, which makes it an ideal candidate for measurement using differential optical absorption spectrometry (see Chapter 11). With this technique, enhanced levels of OCIO have been measured in both the Antarctic and the Arctic (e.g., Solomon et al., 1987, 1988 Wahner and Schiller, 1992 Sanders et al., 1993). From such measurements, it was estimated that about 20-30% of the total ozone loss observed at McMurdo during September 1987 and 1991 was due to the CIO + BrO cycle, with the remainder primarily due to the formation and photolysis of the CIO dimer (Sanders et al., 1993). The formation of OCIO from the CIO + BrO reaction has also been observed outside the polar vortex and attributed to enhanced contributions from bromine chemistry due to the heterogeneous activation of BrONOz on aerosol particles (e.g., Erie et al., 1998). 

These are the Fourier components of the polarization vector which are connected with the oscillations of the ions that are present in eqns. (44)-(46). In addition to this polarization which results from the motion of the nuclei, purely electronic polarization (i.e. the polarization of electrons at equilibrium positions of the nuclei) is also of importance. In the frequency region below the optical range, the purely electronic polarization can be expressed through the optical dielectric permeability (i.e. the dielectric permeability corresponding to the frequencies which are less than those in the optical absorption region, but exceed those of the nuclei vibrations). Optical frequencies considerably exceed those of the nuclear vibrations therefore, in the optical frequency region the nuclei do not, in practice, contribute to polarization. The connection of the Fourier component of purely electronic polarization with that of the induction of the electric field has the usual form... 

Vapour pressures for a number of atmospherically relevant condensed systems have been measured with mass spectrometry. These systems include hydrates of HC1, HjS04 and HNO, supercooled liquids and pure water-ice, as well as the interactions of HC1 vapour with die solids, ice and NAT [23,47,50-55]. Vapour pressure measurements over HNOj/HjO hydrates have also been made using infrared optical absorption with light originating from a tunable diode laser [29]. This technique allowed the identification of the metastable NAD in presence of the more stable NAT under temperature and vapour pressure conditions near to those found in the polar stratosphere. Vapour pressures of Up, HN03, HC1, HBr over supercooled aqueous mixtures with sulfuric acid have been calculated using an activity model [56]. It provides a parameterized model for vapour pressures over the stratospheric relevant temperatures (185-235 K). 

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