Spectral Attributes

Luminescent changes with shifts in pH usually are due to reconfiguration of a fluorophore s tt-electron cloud if an atom on the ring system becomes protonated or unprotonated. Since the BODIPY structure lacks an ionizable group, alterations in pH have no effect on its spectral attributes. 

Dynamic Texture Attributes. Dynamic texture attributes are generated from the original seismic cube. The volume reflection spectrum (VRS) attributes realize spectral analysis of the reflectivity response for each seismic trace [39]. Each trace is characterized in terms of its eigenvalue (spectral attribute) and the associated eigenvector (orthogonal, polynomial), to a > proximate the reflection amplitude along the trace in a least squares sense. For texture mapping a set of discrete spectral VRS coefficients is combined into a composite spectral representation. 

Line shifts as a function of pressure have been studied for pentacene and terrylene in /i-teriDhenyl [98, 99]. Botli exhibited linear and reversible spectral red shifts witli increasing pressure. Modest variations (factors of 1.3-1.6) in tlie pressure shifts among molecules were attributed to slightly different local environments. 

Wlrile tire Bms fonnula can be used to locate tire spectral position of tire excitonic state, tliere is no equivalent a priori description of the spectral widtli of tliis state. These bandwidtlis have been attributed to a combination of effects, including inlromogeneous broadening arising from size dispersion, optical dephasing from exciton-surface and exciton-phonon scattering, and fast lifetimes resulting from surface localization 1167, 168, 170, 1711. Due to tire complex nature of tliese line shapes, tliere have been few quantitative calculations of absorjDtion spectra. This situation is in contrast witli tliat of metal nanoparticles, where a more quantitative level of prediction is possible. 

In 1868, within a decade of the development of the spectroscope, an orange-yeUow line was observed in the sun s chromosphere that did not exactiy coincide with the D-lines of sodium. This line was attributed to a new element which was named helium, from the Greek hellos, the sun. In 1891 an inert gas isolated from the mineral uranite showed unusual spectral lines. In 1895 a similar gas was found in cleveite, another uranium mineral. This prominent yellow spectral line was then identified as that of helium, which to that time had been thought to exist only on the sun. In 1905 it was found that natural gas from a well near Dexter, Kansas, contained nearly 2% helium (see Gas, natural). 

Kastner et al. [25] also reported Raman spectra of cathode core material containing nested tubules. The spectral features were all identified with tubules, including weak D-band scattering for which the laser excitation frequency dependence was studied. The authors attribute some of the D-band scattering to curvature in the tube walls. As discussed above, Bacsa et al. [26] reported recently the results of Raman studies on oxidatively purified tubes. Their spectrum is similar to that of Hiura et al. [23], in that it shows very weak D-band scattering. Values for the frequencies of all the first- and second-order Raman features reported for these nested tubule studies are also collected in Table 1. 

Malhotra et al. (5pyrrolidine enamine of 3-methyl-cyclohexanone, prepared under equilibrating conditions, is a 3 7 mixture of A and A isomers (67 and 68) on the basis of NMR spectral data. The preponderance of the A isomer in the mixture was attributed to strain between the equatorial methyl group and the vinylic hydrogen atom... 

Anhydrous quinazoline hydrochloride absorbs one molecule of water readily, and. the product is difficult to dehydrate completely even in a high vacuum at 60°. Infrared spectral data suggest that this water is covalently bound because of (o) the absence of several bands in the spectrum of the hydrate which are present in the spectrum of the anhydrous hydrochloride and (6) the presence of extra bands at 1474 and 1240 cm that have been attributed to C— H and O— H bending vibrations of the — CHOH group. 

The induced absorption band at 3 eV does not have any corresponding spectral feature in a(co), indicating that it is most probably due to an even parity state. Such a state would not show up in a(co) since the optical transition IAK - mAg is dipole forbidden. We relate the induced absorption bands to transfer of oscillator strength from the allowed 1AS-+1 (absorption band 1) to the forbidden 1 Ak - mAg transition, caused by the symmetry-breaking external electric field. A similar, smaller band is seen in EA at 3.5 eV, which is attributed to the kAg state. The kAg state has a weaker polarizability than the mAg, related to a weaker coupling to the lower 1 Bu state. 

Our sun is, of course, a star. It is a relatively cool star and, as such, contains a number of diatomic molecules (see Figure 25-3). There are many stars, however, with still lower surface temperatures and these contain chemical species whose presence can be understood in terms of the temperatures and the usual chemical equilibrium principles. For example, as the star temperature drops, the spectral lines attributed to CN and CH become more prominent. At lower temperatures, TiO becomes an important species along with the hydrides MgH, SiH, and A1H, and oxides ZrO, ScO, YO, CrO, AlO, and BO. 

The checkers found that a fraction, b.p. 45-71° (18 mm.), had the following spectral properties infrared (carbon tetrachloride) no absorption in the 3300-1600 cm.-1 region attributable to OH, C=0, or C=C vibrations proton magnetic resonance (chloroform-d) <5, multiplicity, number of protons, assignment 3.1-4.2 (multiplet, 4, CH—Cl, CH—O, and C//2—O), 1.0-2.5 (multiplet, 7, GH3 and 2 x C//2)-Thin layer chromatographic analysis of this fraction on silica gel plates using chloroform as eluent indicated the presence of a major component (the cis- and fraus-isomers), Rf = 0.60, and a minor unidentified component, Rf = 0.14. 

Fig. 15. The low-frequency vibrational mode spectrum for 8CB in its smectic phase. The broad and weak spectral feature at about 8 cm has been attributed to intermolecular forces extending across smectic layers...

Astronomers use spectroscopy to identify the composition of the sun and other stars. A striking example is the discovery of the element helium. In 1868, astrono-mers viewing a solar eclipse observed emission lines that did not match any known element. The English astronomer Joseph Lockyer attributed these lines to a new element that he named helium, from hellos, the Greek word for the sun. For 25 years the only evidence for the existence of helium was these solar spectral lines. 

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