Band shifts

The absorption band at 300 nm may also be associated with alkah ions, possibly the result of a trapped electron stabili2ed by an alkah ion. The band shifts to longer wavelengths when heavier alkah ions are present, and growth rates for the band show a definite dependence on the type of alkah (205,209). 

These curves were obtained after 14-21 days incubation at 1 °C. By heating, the 198 nm band shifts to less negative and the band at 223 nm to more negative values (Fig. 11). 

Plutonium(IV) polymer has been examined by infrared spectroscopy (26). One of the prominent features in the infrared spectrum of the polymer is an intense band in the OH stretching region at 3400 cm 1. Upon deuteration, this band shifts to 2400 cm 1. However, it could not be positively assigned to OH vibrations in the polymer due to absorption of water by the KBr pellet. In view of the broad band observed in this same region for I, it now seems likely that the bands observed previously for Pu(IV) polymer are actually due to OH in the polymer. Indeed, we have observed a similar shift in the sharp absorption of U(0H)2S0ir upon deuteration (28). This absorption shifts from 3500 cm 1 to 2600 cm 1. 

Band Shifts (Elastic Collisions with Atom Transfer)... 

Concerning the role of the active site Fe ion, it has been argued that the observed FTIR band shifts (typically 20 cm ) resulting from one-electron redox changes are too small to correspond to metal-based redox processes, whose band shifts should amount to about 100 cm per electron (90, 101). There is, however, one example where the shift in f(CN ) upon one-electron reduction of a Fe(III) center is only of... 

Nevertheless, the band-shift rule can be used to identify the geometries of each of the He2 Br2(X, v" = 0) conformers. Since the T-shaped He Bt2 feature associated with transitions of the (l,0)He Bt2 conformer is observed at - -4cm from the monomer band origin,... 

The action spectrum plotted in Fig. 7c was recorded in the Br2 B X, 14—0 region. Features associated with transitions of Hes Br2 complexes are expected to become prominent in this spectrum since the Av = —3 product is being probed. Again following the band-shift rule the features associated with transitions of the (3,0)He Br2 and (2,l)He Br2 conformers are observed at about +4 cm from the (2,0)He Bt2 and (l,l)He Br2 features. Since the (0,l)He- Br2 feature is shifted by about +10cm from the monomer band origin, and the (l,l)He Br2 feature is found at about +14cm, the weak feature observed at about +24 cm is tentatively attributed to transitions of the... 

The ability to stabilize different conformers of the higher order, ground-state Rg " XY complex opens a new avenue for dynamics and energy-transfer studies. Since all of the observed He ICl and He Br2 features follow the band-shift rule the He atoms must not be strongly interacting in either the ground or excited electronic states. It therefore seems likely that transitions of the... 

This expression indicates that the change in hybridization energy is opposite and proportional to the shift of the d band center. Thus, if the d band shifts upwards the hybridization energy increases and vice versa. Strain and the associated shift of the d band can be brought about by growing the desired metal pseudomorfically on another material with a different lattice constant. The term pseudomorfic means that the overlayer grows with the same lattice constant as the substrate. The overlayer may thereby be strained or compressed depending on the lattice constants of the two materials. 

Figure 6.33. Trends in reactivity for an overlayer deposited pseudomorfically on a substrate. The diagonal gives the position of the center of the d band for the pure metals. The other numbers indicate the shift of the d band by formation of a pseudomorfic overlayer, irrespective ofw/hether it can be realized. Notice that in the low/er left-hand corner the d bands shift upw/ards, leading to higher...

The same theory, i.e. Eqs. (86) and (87), allows us to understand why CO and similar molecules adsorb so much more strongly on under-coordinated sites, such as steps and defects on surfaces. Since the surface atoms on these sites are missing neighbors they have less overlap and their d band wUl be narrower. Consequently, the d band shifts upwards, leading to a stronger bonding. 

The EMIRS and SNIFTIRS methods provide the IR vibrational spectra (really the difference spectra - see later) of all species whose population changes either on the electrode surface or in the electrical double layer or in the diffusion layer in response to changing the electrode potential. Spectra will also be obtained for adsorbed species whose population does not change but which undergo a change in orientation or for which the electrode potential alters the Intensity, the position or shape of IR absorption bands. Shifts in band maxima with potential at constant coverage (d nax 6 very common for adsorbed species and they provide valuable information on the nature of adsorbate/absorbent bonding and hence also additional data on adsorbate orientation. 

Figure 5 shows a series of infrared spectra taken during the TPR of NO with CH4. At temperatures less than 350 °C the spectra in Figure 5 are virtually identical to those for NO TPR seen in Figure 4. Above 350 °C the nitrosyl bands are more intense in the presence of CH4. A new peak appears at 2270 cm when the temperature is raised to 400 °C and above, and another one appears at 2173 cm at 450 °C. Neither of these bands was observed when the reaction mixture was passed over Na-ZSM-5. When 5NO was substituted for NO, the two bands appeared at 2256 cm- and 2144 cm, and when 3CH4 was substituted for 12CH4, the bands shifted to 2237 cm and 2132 cm-. Based on previous studies [32-34], the band at 2270 cm- is best attributed to NCO species adsorbed at Al + sites. The observed shift in the...

The presence of methylenic bands shifted at higher frequency in the very early stages of the polymerization reaction has also been reported by Nishimura and Thomas [114]. A few years later, Spoto et al. [30,77] reported an ethylene polymerization study on a Cr/silicalite, the aluminum-free ZSM-5 molecular sieve. This system is characterized by localized nests of hydroxyls [26,27,115], which can act as grafting centers for chromium ions, thus showing a definite propensity for the formation of mononuclear chromium species. In these samples two types of chromium are present those located in the internal nests and those located on the external surface. Besides the doublet at 2920-2850 cm two additional broad bands at 2931 and 2860 cm are observed. Even in this favorable case no evidence of CH3 groups was obtained [30,77]. The first doublet is assigned to the CH2 stretching mode of the chains formed on the external surface of the zeolite. The bands at 2931 and... 

The absorption band shifts to lower energy from top to bottom in the table. Roughly speaking the degree of covalency increases also in this sequence. Therefore it may be thought that we are dealing with one and the same transition. This, however, is unlikely. The literature contains many different, and sometimes not firmly based, assignments. 

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... 

To get site-specific information about this unfolding process, a similar series of peptides, Ac-(AAAAK)3AAAA-YNH2, was sequentially labeled with 13C on the C=0 of four Ala residues, first on those at the N terminus, and then sequentially for the three other tetra-Ala positions (Decatur and Antonie, 1999). IR results showed a band shifted down 40 cm-1 from the amide F, which formed a clearly resolved band... 

Different aromatic hydrocarbons (naphthalene, pyrene and some others) can form excimers, and these reactions are accompanying by an appearance of the second emission band shifted to the red-edge of the spectrum. Pyrene in cyclohexane (CH) at small concentrations 10-5-10-4 M has structured vibronic emission band near 430 nm. With the growth of concentration, the second smooth fluorescence band appears near 480 nm, and the intensity of this band increases with the pyrene concentration. At high pyrene concentration of 10 2 M, this band belonging to excimers dominates in the spectrum. After the act of emission, excimers disintegrate into two molecules as the ground state of such complex is unstable. 

Electrophoretic band-shift The reaction mixtures contain 20 pi of 50 mM imidazole-HCl (pH 7.5) buffer, 50 mM NH4C1, 10 mM Mg acetate, and 1 pM each IF2 and f[35S]Met-tRNAmetf. After 10 min incubation at 37°,... 

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