Polarized Raman

Figure Bl.3.8. A WMEL diagram for die three-colour fifth order qiiasi-Ramaii echo . As usual, the first pair of field actions creates the Raman coherence which is allowed both to dephase and walk off with time. This is followed by a second pair of field actions, which creates a different but oppositely phased Raman coherence (now hf) to the first. Its frequency is at oi - oij = Provided that frequencies are identified with an inliomogeneous distribution that is similar to those of the frequencies, then a quasi-rephasing is possible. The fifth field action converts the newly rephased Raman polarization into the quasi-echo at co = 2(b, — CO, = CO, + CO,...

I.r. and Raman spectra were interpreted in terms of linear anions. In addition, far-i.r. and Raman spectra of the solid [AuXL] (L = PPh3 or AsPh3 X = Cl or Br) and Raman polarization data in solution have enabled identification of the Au—P and Au—As stretching modes.223... 

Ionic nitrate D3h has 4 vibrations (3 IR active 1 Raman active), coordinated nitrate C2V has 6 IR active, and 6 Raman active vibrations. The doubly degenerate V4 band of ionic nitrate (700 cm-1) is split into V3 and V4 upon coordination. Further Raman polarization studies can distinguish between monodentate from bidentate nitrate and bridging nitrate groups. As an example La(HMPA)3(N03)3 has both ionic and coordinated nitrate [161]. 

In Eq.(23), J and K are the rotational quantum numbers for the total angular momentum and the component projected to the molecular principal axis, p is the anisotropy of the Raman polarization tensor, pj is the thermal rotational distribution function in the initial state, and N specifies the selection rule of the rotational Raman transitions. (J)=0 if J<0 and 4(J)=1 or all other values of J,... 

The structural parameters, energies, and vibrational frequencies of 2-methylthiobenzothiazole were obtained by ab initio RHF calculations using the 6-31G basis set for various conformations. A detailed assignment of most of the observed bands was proposed from the IR dichroism, Raman polarization data, and frequency calculations <2000SPL535>. 

Several aspects of Raman polarization measurements are of value for chemical analysis. First, polarization provides a means to determine the symmetry... 

Interest in Zr carbonates in part originates from their presence in nuclear waste.495 Equilibrium constants for the formation of [M(C03)4]4 have been measured,496 and the coordination mode and kinetic behavior have been determined by dynamic NMR and Raman polarization studies.495 The interactions of carbonate ions with Zr has been investigated by potentiometry, NMR spectroscopy,497 and electrospray mass spectrometry.498 Although four-coordination modes are possible, the data suggested a bidentate binding mode for the carbonates in [Zr(CC)3)4]4. ... 

The use of polarized light to generate contrast between bone components provides information on the spatial distribution of bone components and their orientation. Kazanci et al. used Raman polarized imaging to examine the distribution of mineral and matrix constituents around osteons, and showed that the POi Vi and amide I bands are highly orientation-dependent, whereas the amide III and POi V2 and V4 are less orientation-dependent [35]. Orientation effects are nicely illustrated in Figure 4.2 [36]. The POi Vj amide I ratio coincides with the orientation of the lamellae the same lamellae have different contrasts, depending on the polarization of the excitation light and the orientation of the specimen. 

The infrared spectrum of quinazoline and other diazanaphthalenes were measured, and the vibrational fundamentals were assigned from Raman polarization data. The Raman spectrum of quinazoline in aqueous solution has fourteen bands that appear to be polarized. All the band frequencies, except for those at 1330 and 1334 cm were consistent with the frequencies assigned as fundamentals in the spectrum of naphthalene. The infrared spectra of several quinazolin-4(3H)-ones and their 3-acetyl, 3-acetoxy, and 3-hydroxy derivatives were examined at wave numbers lower than 3000 cm Bands due to NH stretching vibrations provided evidence for cyclic dimeric association between molecules. The zwitterionic structure (3) was proposed for 3-hydroxyquinazolin-4-one. ... 

IR spectra of pyridazines and polypyridazines were studied with respect to interactions with the side chain. The IR spectral shift due to hydrogenbonding between methanol and pyridazine (and other azines) was determined the Av was compared with the pK . In connection with the structure of maleic hydrazide and its methyl derivatives, the Raman spectrum of the 1,2-dimethyl derivative was recorded and helped to explain the anomalously low reported IR carbonyl frequency. The laser Raman polarization spectrum of the lattice vibrational region of pyridazine was reported. ... 

The lattice-mode spectrum has been examined by Iqbal and Malhotra [79], who obtained both IR and polarized Raman results. Their observations and assignments are summarized in Table X along with other recent data [46, 80]. The Raman polarization data yield a clear separation of Ag and Bg modes. On the basis of frequency and intensity, the Bg species modes at 153 and 206 cm" are most probably rotatory in nature. Further differentiation of translational and rotatory modes does not appear to be feasible unless isotope substitution studies or CNIS measurements are performed. The general agreement between TO modes observed by IR transmission and reflection is rather good. The absence of the 42 and 64 cm modes in the IR reflection data is not necessarily of... 

Molecules like 02H take the nonplanar Q structure (twisted about the 0-0 bond by ca. 90"), whereas N2F2 and [N203] exist in two forms /mm-planar (C2/,) and cis-planar (C21.). Figure 11-7 shows the six normal modes of vibration for the C2, and C2 structures. The selection rules for these two structures are different only in the vibration, which is infrared inactive and Raman depolarized in the planar model but infrared active and Raman polarized in the nonplanar model. 

As is shown in Table III-26, normal coordinate analysis predicts that the highest-frequency CO stretching band belongs to the species in the unidentate and the A, species in the bidentate complex. Elliott and Hathaway studied the polarized infrared spectra of single crystals of [Co(NHj)4C03]Br and confirmed these symmetry properties. As will be shown later for nitrafo complexes, Raman polarization studies are also useful for this purpose. 

Id usually appears as a thin film on a glass surface, and until now we have not succeeded in obtaining a single crystal for the X-ray analysis. However, there are some reasons to speculate about its structure. For disilenes of the type RR Si=SiR R, photochemical cis-tram isomerization in solution was shown to occur [11], the trans isomer being predominant under equilibrium conditions. Of course, symmetrically substituted 1 crumot have real cis—trans isomers, but, by analogy, a similar equilibrium with predominance of a conformer, close to the tram one, seems likely in solution. This assumption is eonfirmed by Raman polarization measurements for a solution of 1 in hexane, because the selection mles observed for the conformer predominant in solution are consistent with C2h symmetry, that is, with a quasi-/ra s structure of this conformer [12]. As both the Raman and UV-Vis absorption and fluorescence spectra of solid Id are similar to those of 1 in hexane solution [1,12], we can suggest for Id also a quasi-/ra/is structure as shown in Fig. I. 

We can now complete the assignment for PF5, by distinguishing between the a and e" modes. The two a modes will be polarized (Table 8.3), although one of the a modes of PF5 gives a depolarization ratio elose to the limiting value The third Raman band without an IR counterpart must be of e" symmetry it will be depolarized, as wiU be the bands due to the e modes. Raman polarization is discussed in more detail in the online supplement to Chapter 8. 

When making Raman polarization measurements with a microscope objective, the condition of normal incidence is not valid, except exactly at the center of the objective, such that the spectra are perturbed by the presence of (a) broadening of peaks due to the continuum of angles of incidence and (b) extra peaks associated with other polarization configurations. The situation is worse with higher magnifications and better with the macro configuration. 

The copolymer shows a D-E hysteresis loop. The value of the ramanent polarization is quite large, le.. 200-7D0 mOin at 1QS C due to the dipole polarization. At higher temperatures, DC conduction ot took impurities would siqterinqxKc on the dipole orientation current. Therefore, we attempted to conduct measurements at low temperatures, and recorded a D-E hysteresis loop that has a remanent polarization of 30 mOm (Fig. 15) (34). This value of remanent polarization coincides with the integratioo of thermally depolarizatioo current, which may be attributed to the CN dipole orientation. 

In-plane modes 8 Ag(Raman-polarized fl-depen-dent) + 8 ig(Raman-dep) + 7 fi2u(IR) + 7 fi3u(IR)... 

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