Sites spectrum

Figure 4 Schematic showing both correlated and uncorrelated transitions in an inhomogeneously broadened electronic spectrum. Each single site spectrum shows relatively narrow, homogeneously broadened features. Correlated features track with the energy of a narrow electronic origin. Noncorrelated sidelines appear at any energy within its full, inhomogeneously broadened band...

Fig. 16A-D. Mechanical switching in rotaxanes. A Rotaxanes may exist in isomeric states by the movement of the ring component between dissymmetric sites on the string component. B A redox- or pH-switchable [2]rotaxane. While the cyclophane complexes the native benzidine site (spectrum, curve a), the reduced or protonated benzidine repels the cyclophane, causing it to move to the dioxybiphenylene site (spectrum, curve b). C An azobenzene-based switchable [2]rotaxane. The cyclodextrin ring complexes the azobenzene site in the trans-state, but it is repelled from the ds-azobenzene. The state of the system is measurable by circular dichroism (plot). D A pH-switchable rotaxane. When the amine on the string component is protonated, it complexes the crown ether ring by hydrogen-bonding interactions (40a). When the amine is deprotonated, however, the ring component moves to the bipyridinium unit, where it is complexed by n donor-acceptor interactions (40b). The plots in B and C are adapted from [67] and [69], respectively, with permission...

Solid-state ion exchange with CaCl2/H-MOR and MgC /H-MOR was also monitored by IR. Figure 7 demonstrates, as an example, the removal of acidic OH groups (spectrum 2a) in H-MOR due to replacement of the protons by Ca +. Subsequent pyridine adsorption gave rise to a sharp band at 1446 cm typical of pyridine coordinatively bonded to calcium cations and a smaller band at 1455 cm which is due to pyridine attached to true Lewis sites (spectrum 2b). Most likely, both types of pyridine coordination contributed to the small signal at 1610 cm. Note, however, that only a very weak pyridinium ion band at 1540 cm was observed. Another sample, which had been prepared via solid-state ion exchange (spectrum 2a), was contacted with small amounts... 

TiFc204 is an inverse spinel, Fe +[Fe +Ti +]04, and shows a large quadru-pole splitting above the Neel temperature of 140 K [24, 26, 62, 63]. The A site spectrum is not resolved from the B site spectrum in the range from 140 to 800 K, and clearly the A site does not have cubic symmetry [63]. Each tetrahedral Fe " " ion has and (12 — y)Fe octahedral sites in the... 

The four-site spectrum is plotted in Figure 1 where the + and the - denote states which are symmetric and antisymmetric with respect to a reflection through a plane at the midpoint and perpendicular to the axis of the fiber. We note that for x < 1, the linear... 

Still another type of adsorption system is that in which either a proton transfer occurs between the adsorbent site and the adsorbate or a Lewis acid-base type of reaction occurs. An important group of solids having acid sites is that of the various silica-aluminas, widely used as cracking catalysts. The sites center on surface aluminum ions but could be either proton donor (Brpnsted acid) or Lewis acid in type. The type of site can be distinguished by infrared spectroscopy, since an adsorbed base, such as ammonia or pyridine, should be either in the ammonium or pyridinium ion form or in coordinated form. The type of data obtainable is illustrated in Fig. XVIII-20, which shows a portion of the infrared spectrum of pyridine adsorbed on a Mo(IV)-Al203 catalyst. In the presence of some surface water both Lewis and Brpnsted types of adsorbed pyridine are seen, as marked in the figure. Thus the features at 1450 and 1620 cm are attributed to pyridine bound to Lewis acid sites, while those at 1540... 

First, it is possible to excite a chromophore corresponding to the active site, and detennine which modes interact with it. Second, by using UV excitation, the amino acids with phenyl rings (tryptophan and tyrosine, and a small contribution from phenylalanine) can be selectively excited [4], The frequency shifts in the resonance Raman spectrum associated with them provide infomiation on their enviromnent. 

P correlation of two inorganic hydrated phosphates, (a) bnishite and (b) a bone, are shown [48]. In both cases two phosphorus sites that completely overlap in the 1D MAS spectrum are clearly visible in the 2D spectrum. 

The set of equations in (16) are greatly simplified if we make some assumptions which allow the exciton and phonon site nondiagonal matrix elements to be neglected. In the case of an Einstein phonon spectrum... 

In one instrument, ions produced from an atmospheric-pressure ion source can be measured. If these are molecular ions, their relative molecular mass is obtained and often their elemental compositions. Fragment ions can be produced by suitable operation of an APCI inlet to obtain a full mass spectrum for each eluting substrate. The system can be used with the effluent from an LC column or with a solution from a static solution supply. When used with an LC column, any detectors generally used with the LC instrument itself can still be included, as with a UV/visible diode array detector sited in front of the mass spectrometer inlet. 

In the middle of the accuracy spectrum are the models based on approximately 35% sequence identity, corresponding to 85% of the Ca atoms modeled within 3.5 A of their correct positions. Eortunately, the active and binding sites are frequently more conserved... 

This compound has two crystallographically distinct vanadium sites. While the static spectrum is a superposition of two powder patterns of the kind shown in Figure 3, MAS leads to well-resolved sharp resonances. Weak peaks denoted by asterisks are spinning sidebands due to the quadrupolar interaction. 

The absorption spectrum of this nonstoichiometric phase forms the basis for the formerly much-used qualitative test for zinc oxide yellow when hot, white when cold . Alternatively, anion sites can be left vacant, e.g. ... 

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