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INDEX vibrational spectra

Since the spatial configuration of a lattice with excitation of long-wave acoustical vibrations can be described by the dynamical displacement tensor u p q and dynamical displacements of sublattices w k,qj (with the index of the acoustical branch of the vibrational spectrum), which are represented as... [Pg.327]

FIGURE 2.1 Energy of the 0-0 vibrational transition in the principal electronic absorption spectrum of violaxanthin (l Ag-—>1 BU+), recorded in different organic solvents, versus the polarizability term, dependent on the refraction index of the solvent (n). The dashed line corresponds to the position of the absorption band for violaxanthin embedded into the liposomes formed with DMPC (Gruszecki and Sielewiesiuk, 1990) and the arrow corresponds to the polarizability term of the hydrophobic core of the membrane (n = 1.44). [Pg.20]

As is seen from Table 13, cholesteric copolymers display a maximum of selective light reflection ( w) in an IR- or a visible part of the spectrum. By varying the composition of a copolymer, it is possible to vary Xmax, in accordance with the stipulation max = nP, is proportional to the pitch P of the helical structure of a LC polymer (n — is the refractive index). The pitch of the helix in cholesteric copolymers is usually decreased, when the temperature is raised 105) (at temperatures above Tg), which is equally common for low-molecular cholesterics142) (Fig. 23a). The observed fact that the helix pitch for LC copolymers 2.1-2.3 (Table 13, Fig. 23b) is increased, is rather unusual but explicable within the theoretical views regarding vibrational movement of macromolecular fragments and their conformational mobility 60). [Pg.224]

The ultraviolet spectrum of pyrazine in cyclohexane shows maxima at 260 nm (corresponding to a tt-tt transition) and 328 nm (corresponding to a n-7r transition) in each case with vibrational fine structure the coefficients of molecular extinction are 5600 and 1040, respectively.78,79 Substitution of halogen has a bathochromic effect on the ultraviolet spectrum of pyrazine.80 A useful index of the ultraviolet and visible spectra of pyrazine derivatives is available for the period from 1955 to 1963.81 The far-ultraviolet spectrum of pyrazine... [Pg.108]

The High Frequency dielectric constant is measured at the frequencies faster than the vibrational motion of ions. It is applicable to the visible region of the spectrum. It determines refractive index which governs the transmission of light in transparent media. [Pg.142]

FI5. N. N. Greenwood, E. J. F. Ross, and B. P. Straughan, Index of Vibrational Spectra of Inorganic and Organometallic Compounds, Volume 1, 1935-1960. Butterworth, London, 1972. This publication arose as a result of literature surveys carried out for B6.1. Compounds are arranged by molecular formula, and for each, the physical state, type of spectrum (IR, Raman, etc.), and range are listed. [Pg.388]

The IR spectrum of the unsubstituted cydopropenylium ion exhibits only four bands at 3105, 1276, 908 and 736 cm , as expected from the Djij-symmetry. The band at 1276 cm is due to an E ring deformation vibration of the central three-membered ring, which is generally observed as a strong band in the range of 1400 to 1490 cm for the aryl- and alkyl-substituted derivatives (Table 2). The frequency of this band for the trimethyl-, tri-zc-rt-butyl, triphcnyl, and unsubstituted cydopropenylium ions exhibits a linear correlation with the index of the cation s thermodynamic stability such as For heteroatom-substituted derivatives... [Pg.3080]

The importance of quadratic terms emerges, however, from the analysis of the IR spectrum of hquid water (Ch. 9). hi that case they do not only involve the stretching intermonomer vibration of an H-bond, but also one or both of the bending intermonomer vibration(s) Qg and/or Q. For simphcity we represent both 0 and y by a single index 8 for bending intermonomer vibrations. The dependence of co on intermonomer modes then takes on the form... [Pg.143]

With the ever-increasing need to improve quality and productivity in the analytical pharmaceutical laboratory, automation has become a key component. Automation for vibrational spectroscopy has been fairly limited. Although most software packages for vibrational spectrometers allow for the construction of macro routines for the grouping of repetitive software tasks, there is only a small number of automation routines in which sample introduction and subsequent spectral acquisition/data interpretation are available. For the routine analysis of alkali halide pellets, a number of commercially available sample wheels are used in which the wheel contains a selected number of pellets in specific locations. The wheel is then indexed to a sample disk, the IR spectrum obtained and archived, and then the wheel indexed to the next sample. This system requires that the pellets be manually pressed and placed into the wheel before automated spectral acquisition. A similar system is also available for automated liquid analysis in which samples in individual vials are pumped onto an ATR crystal and subsequently analyzed. Between samples, a cleaning solution is passed over the ATR crystal to reduce cross-contamination. Automated diffuse reflectance has also been introduced in which a tray of DR sample cups is indexed into the IR sample beam and subsequently scanned. In each of these cases, manual preparation of the sample is necessary (23). In the field of Raman spectroscopy, automation is being developed in conjunction with fiber-optic probes and accompanying... [Pg.540]

The crystal structure of YF3 at room temperature is Pnma, with Y ions in sites of Cs symmetry (Wyckoff, 1%4). A higher temperature hexagonal form has also been observed (Sobolev and Fedorov, 1973). The index of refraction is 1.550 at the sodium D line doublet (X = 0.589 p,m) and the dielectric constant is 10.0 at / = 760 kHz (Dulepov et al., 1976). The polarized infrared spectrum of YF3 has been obtained and the lattice vibrations have been analyzed and assigned to symmetry species (Rast et al., 1969). Electron-beam and ultraviolet excitation of rare-earth doped YF3 has determined the energy separation of the configurations 4f"" 5d and 4f" for several rare earths (Yang and DeLuca, 1976). [Pg.532]

Infrared-based techniques are used to identify molecules on the surface. IR radiation is used to excite vibrational modes in molecules in the gas phase or adsorbed on a surface. The transmitted or reflected IR spectrum can be analyzed in a spectrometer. Considerable improvement in the sensitivity can be achieved by use of Fourier transform infrared (FTIR) spectroscopy. Attenuated total reflection (the ATR-FTIR method) inside a crystal (germanium) of high refractive index can be used to further enhance the surface sensitivity (using the evanescent field). [Pg.3121]


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See also in sourсe #XX -- [ Pg.193 ]

See also in sourсe #XX -- [ Pg.178 ]

See also in sourсe #XX -- [ Pg.44 ]

See also in sourсe #XX -- [ Pg.193 ]




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INDEX spectra

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