Raman inactive

The antisymmetric stretching vibration. The molecule loses its original symmetry during the vibration. At the two extrema of the vibration the shapes of the molecule will be identical. Because the molecular polarizability is essentially the summation of all bond polarizabilities and is independent of direction along the internuclear axis, it will have identical values at the extrema. Consequently, the vibration is Raman inactive. 

Application of similar reasoning to the case of the bending mode of COj would indicate that the vibration is Raman inactive, infrared active. 

In oxidized Rieske proteins, a larger number of peaks are observed that have been attributed to vibrations of the iron-sulfur core this is indicative of the reduced symmetry of the iron-sulfur core in Rieske proteins since ungerade vibrations are Raman-inactive in the centro-symmetric (in first approximation) [2Fe-2S]-Cys4 core (point group D2h or Cih) while the corresponding modes are Raman-active in C2 symmetry. The characteristic peak of the SL mode of proteins con-... 

The IR spectra of silicon oxides, in the framework region mode, is dominated by a strong absorption around 1000 cm due the anti-symmetric stretching of the Si - 0 - Si unit (Raman inactive mode) and by a less intense absorption around 800cm due the symmetric stretching of the Si-O-Si unit (Raman active mode). In the transparency window between these two modes, the IR spectra of TS-1 shows an additional absorption band located at 960 cm ... 

Similarly, the first-order expansion of the p° and a of Eq. (5.1) is, respectively, responsible for IR absorption and Raman scattering. According to the parity, one can easily understand that selection mles for hyper-Raman scattering are rather similar to those for IR [17,18]. Moreover, some of the silent modes, which are IR- and Raman-inactive vibrational modes, can be allowed in hyper-Raman scattering because of the nonlinearity. Incidentally, hyper-Raman-active modes and Raman-active modes are mutually exclusive in centrosymmetric molecules. Similar to Raman spectroscopy, hyper-Raman spectroscopy is feasible by visible excitation. Therefore, hyper-Raman spectroscopy can, in principle, be used as an alternative for IR spectroscopy, especially in IR-opaque media such as an aqueous solution [103]. Moreover, its spatial resolution, caused by the diffraction limit, is expected to be much better than IR microscopy. 

Exceptions include coherent IR-active (but Raman-inactive) phonons observed as... 

Numerous SERS studies of adsorbed molecules have appeared in the literature. Obviously, it is a useful method for the identification of species at the interface, and its inherent surface sensitivity is an attractive feature. In this context it should be noted that the adsorption of a molecule can change the selection rules for Raman scattering, and modes that are Raman inactive in the isolated molecule may show up in SERS. 

For local symmetries with a center of symmetry (see Section 7.2), an infrared active vibration (phonon) is Raman inactive, and vice versa. This rule is usually known as the mutual exclusion rule. 

Fig. 14 Temperature dependence of modes observed in ST018. The soft u mode closed circles above Tc) in the tetragonal Dih phase is divided into two modes presented by open circles (below T ) and closed circles (at Td. Closed squares and open squares denote the modes split from the doubly degenerated Eg mode. Closed triangles above Tc indicate the Raman-inactive Aiu mode observed by local symmetry breakdown [11]...

It should be noted that the Raman-inactive soft mode is observed in the temperature region above Tc. A spectral shape completely different from that of the Lorentz-type peak function indicates the defect-induced Raman scattering (DIRS) in the paraelectric phase of ST018. When centrosymmetry is locally broken in the paraelectric phase, the nominally Raman-inactive soft mode is optically activated locally to induce DIRS in the soft mode. 

The rule of mutual exclusion states that for a molecule with a center of symmetry, a given vibrational transition cannot appear in both the IR and Raman spectra. (For the proof, see Chapter 9.) Some fundamentals may be both IR and Raman inactive their frequencies can often be determined from IR or Raman combination bands. 

The Kekule mode of benzene is the skeletal b2u mode a i4, which has been discussed all along and is shown in Scheme 34a. Another b2u mode is the hydrogenic movement shown in in Scheme 34 b and is labeled as co 15. These modes are both IR and Raman inactive for DSh benzene in the ground state. The electronic transition to the 11 B2u excited state is disallowed, and hence, the observations of the b2u... 

Both A - and Ei-modes are Raman and IR active. The two nonpolar E2-modes E and E are Raman active only. The Bi-modes are IR and Raman inactive (silent modes). Phonon dispersion curves of wurtzite-structure and rocksalt-structure ZnO throughout the Brillouin Zone were reported in [106-108]. For crystals with wurtzite crystal structure, pure longitudinal or... 

The Flu-mode is polar and splits into TO and LO modes. The Fiu-mode is IR active and Raman inactive [109]. 

Figure 3.12 shows typical Raman spectra of several doped ZnO thin films. Additional modes (AM), occurring at to 275, 510, 582, 643, and 856 cm-1 (the first four of them are shown and marked by vertical solid lines in Fig. 3.12), were first assigned to N-incorporation [49-51], because the intensity of these modes was reported to increase with increasing N-content [50], However, the AMs appear also in Raman spectra of ZnO samples doped with other elements (Fig. 3.12a), [48,52,53]). Therefore, it was suggested that the AMs are related to defect-induced modes [48]. Theoretical considerations confirmed this assignment [131]. It was discussed that the AMs could be related to modes of ZnO, which are Raman-inactive within a perfect crystal. Upon doping-induced defect formation, the translational crystal symmetry can be broken, and Raman-inactive modes may become Raman-active. The Raman spectra of the ZnO thin films with transition metals in Fig. 3.12b show a different behavior than those in Fig. 3.12a [43,48], Raman spectra of Fe0.08Zn0.92O contain the above described AMs, but with different intensity ratios. For MnZnO, CoZnO, and NiZnO a broad band between iv 500 cm-1...

Here axx, ocyy, azz, axy, ayz and axz are the components of the polarizability tensor discussed in Section 1.7. If one of these six integrals is nonzero, this vibration is Raman-active. If all the integrals are zero, it is Raman-inactive. 

Vi( i symmetric stretch) at 2917 cm-1 Raman-active, IR-inactive v2 (e symmetric bend 2x degree) at 1534 cm-1 Raman-active, IR-inactive v3 if2 asymmetric stretch, 3 x degree) at 3019 cm-1 Raman-inactive, IR-active v4 (f2 deformation 3x degree) at 1306 cm-1 Raman-inactive, IR-active. 

Vi(biu) (CH symmetric stretch) at 3217 cm-1 Raman-inactive, IR-active v2(ag) (CH symmetric stretch) at 3026 cm-1 Raman-active, IR-inactive v3(b2u) (CH asymmetric stretch) at 3185 cm-1 Raman-inactive, IR-active V4,(b3g) (CH asymmetric stretch) at 3153 cm-1 Raman-active, IR-inactive v5(a ) (CC stretch) at 1623 cm-1 Raman-active, IR-inactive v6(biu) (H-C-H in-plane scissor) at 1413 cm-1 Raman-inactive, IR-active v7(ag) (H-C-H in plane scissor) at 1342 cm-1 Raman-active, IR-inactive vs(b3g) (C-C-H in-plane rocking) at 1167 cm-1 Raman-active, IR-inactive v9(b3u) (H-C-H out-of-plane wag) at 1068 cm-1 Raman-inactive, IR-active vio(b2g) (H-C-H out-of-plane wag) at 1057 cm-1 Raman-active, IR-inactive vn(ag) (H-C-H out-of-plane twist) at 875 cm-1 Raman-inactive, IR-inactive vi2(big) (CH in-plane rock) at 1236 cm-1 Raman-inactive, IR-active v (au) (CH twist) at 1023 cm-1 v-(blg) (CH stretch) at 3013 cm-1... 

Symmetrical vibrations of a molecule with a centre of symmetry do not involve change in dipole moment hence are IR-inactive but are Raman active, while asymmetrical stretching vibrations with a centre of symmetry involve change of dipole moment and hence IR-active but are Raman inactive. 

The vibrational spectrum of the tetramethylammonium cation in the region 150 -550 cm l contains botii torsional and vibrational modes. The vg and V19 vibrational modes of E and T2 symmetry involve C-N-C bond angle bending. These modes are Raman active and have been studied for TMA+ in several zeolite environments, although little change in frequency is observed (51). The V4 and V12 torsional modes involve partial rotation about C - N bonds and form respectively a singlet (A2) and a triplet (Ti) which are both Raman inactive. These torsional modes are directly observed in the HNS spectra and prove to be sensitive to the character of the TMA+ cation (see Table 1) environment(52). 

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