Isotopes band shifts attributed

This broad band at 1500 cm was ascribed by Kaufman. Metin, and Saper-stein [10], to an IR observation of the amorphous carbon Raman D and G bands. This is forbidden by the selection rules, and has been attributed to the symmetry breaking introduced by the presence of CN bonds in the amorphous network. As carbon and nitrogen have different electronegativities, the formation of CN bonds gives the necessary charge polarity to allow the IR observation of the collective C=C vibrations in the IR spectrum. This conclusion was stated by the comparison of spectra taken from films deposited from N2 and N2. In the N2-film spectrum, no shift was observed for the 1500-cm band, whereas all other bands shifted as expected from the mass difference of the isotopes. Figure 25 compares... 

It can be seen from Figures 3.7 and 3.8 that the calculations reproduce very well not only the experimental spectra but also the experimentally observed isotopic shifts indicating a high reliability of the computational method. According to this comparison, definite attribution can be made for even the difficult Raman bands that cannot be assigned based solely on the experimental results. It is, however, necessary to mention at this point that the calculated Raman spectrum provided directly by the ab initio computations correspond to the normal Raman spectrum with the band intensity determined by the polarizability of the correlating vibration. Since the intensity pattern exhibited by the experimentally recorded resonance Raman spectrum is due to the resonance enhancement effect of a particular chromophore, with no consideration of this effect, the calculated intensity pattern may, in many... 

After cocondensation of SiO (1226 cm 1) with alkali metal atoms like Na or K, new bands are detected at 1014 cm 1 (Na) or 1025 cm 1 (K). They can only be attributed to an SiO" anion because of the red shift of the SiO stretching vibration (with respect to that of uncoordinated SiO) and because of different isotopic splittings (28/29/30SiO, Si16/180) [21]. The formation of an ionic species M+(SiO) (M = Na, K) is in line with the results of quantum chemical calculations for the SiO anion (SiO d = 1.49 A, SiO" d = 1.55 A, "electron affinity" SiO + e + 1.06 eV —> SiO") [20]. Taking simple Coulomb interactions into consideration this species is very likely to have a strongly bent structure. The same situation occurs in gaseous NaCN (<(NaNC) = 81.2°) [22],... 

Busca (18b) has evaluated the literature values for infrared bands attributed to coordinated and adsorbed dioxygen species. He concludes that it is very difficult to deduce the nature of the dioxygen coordination from measurements of the frequency shift, Av00, with respect to the stretching frequency of the free molecule. It needs to be stressed that it is also difficult to distinguish between mononuclear and molecular species from measurements of v00, and this can only be achieved by careful interpretation of experiments using 160/180 isotopic mixtures. The absence of such experiments very often accounts for the conflicting attributions in the literature which are discussed in later sections. 

Fig. 8. The c axis polarized second singlet-singlet absorption of As naphthalene in a durene host crystal. The center of the 0-0 band is near 34,550 cm 1 and that of the a (9) addition is near 35,050 cm 1. The fine structure, as narrow as 1 cm"1 in some crystals, is attributed to interference between the second excited singlet state and vibrational additions to the first which have coupling symmetry. The isotopes 1,4, 5,8 — dt, 2,3, 6,7 — d4, and dg-naphthalene produce entirely different structures. For a given isotope, the major structural features change as the separation between the two excited singlets is varied by host-induced shifts, but remain rather similar for hosts that produce the same separation.

As an example of the rotation-vibration band of a diatomic molecule, the nitrogen-broadened spectrum of C 0 is shown in Fig. 4.3-2. An additional band appears, less intense, but shifted, which is attributed to the isotope. Fig. 4.3-3 displays an... 

In the gase phase, the infrared bands are broad (50 cm ), due to the rotational structure, overlapping vibrations, and hot transitions. In the solid state, the rotational motions are quenched, but due to intermolecular (hydrogen bond) and correlation field interactions, the band positions are shifted and the bands are even broader. The infrared absorptions of matrix-isolated molecules are close to the gas-phase frequencies and exhibit a sharp line-like character (half-widths 0.1 to 2 cm ). Hence the spectra of matrix-isolated molecules are less complicated, and, in comparison to gas phase or solid state spectra, the sensitivity and selectivity of detection increase by a factor of about 10 to 100. Closely spaced vibrations attributed to mixtures of similar molecules, such as conformers, rotamers, molecular complexes, or isotopic species, e.g., H C104 and H CI04, are easily distinguished. 

Stong et al. observed the p(Fe-NO) of ferrous Hb-NO at 553 cm in RR spectra (454.5 nm excitation). When IHP (inositol hexaphosphate) was added, an additional band appeared at 592 cm which was attributed to the v Fe-NO) of the five-coordinate Hb-NO resulting from the Fe-N(lm) bond breaking. However, Tsubaki and Yu could not observe this band with 406.7 or 413.3 nm excitation. Recently, Benko and Yu assigned the 554-cm band of ferrous Hb-NO to the S(FeNO) rather than the p(Fe-NO). This new assignment is based on the zigzag isotopic shift pattern in the order of NO(554 )- ... 

The excited states of the Cuzn acceptor in ZnO have been revealed in the absorption and PLE spectra, namely, a characteristic triplet a, p, y at 2.8594, 2.8680, and 2.8733 eV, respectively (Figure 3.21) [109-112]. The a line coincides with the zero-phonon line of the GL [102]. Remarkably, the isotope shift was also observed in the absorption and PLE spectra, at least for a and p lines [111]. These lines have been attributed to transitions Cu (d ) + bv —> (Cu+ (d °), h) in which the excited state is split into three levels corresponding to three valence bands a, h, and c. 

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