Vibrational bands, stretching

H.G. Rubahn, K. Bergmann, The effect of laser-induced vibrational band stretching in atom-molecule coUisions. Annu. Rev. Phys. Chem. 41, 735 (1990)... 

Q are the absorbance and wavenumber, respectively, at the peak (center) of the band, p is the wavenumber, and y is the half width of the band at half height. Liquid band positions ate usually shifted slightly downward from vapor positions. Both band positions and widths of solute spectra are affected by solute—solvent interactions. Spectra of soHd-phase samples are similar to those of Hquids, but intermolecular interactions in soHds can be nonisotropic. In spectra of crystalline samples, vibrational bands tend to be sharper and may spHt in two, and new bands may also appear. If polarized infrared radiation is used, both crystalline samples and stressed amorphous samples (such as a stretched polymer film) show directional effects (28,29). 

In the present work low temperature adsoi ption of fluoroform and CO, were used to characterize surface basicity of silica, both pure and exposed to bases. It was found that adsorption of deuterated ammonia results in appearance of a new CH stretching vibration band of adsorbed CHF, with the position typical of strong basic sites, absent on the surface of pure silica. Low-frequency shift of mode of adsorbed CO, supports the conclusion about such basicity induced by the presence of H-bonded bases. 

Much earlier information on the structure of diazonium ions than that derived from X-ray analyses (but still useful today) was obtained by infrared spectroscopy. The pioneers in the application of this technique to diazonium and diazo compounds were Le Fevre and his school, who provided the first IR evidence for the triple bonds by identifying the characteristic stretching vibration band at 2260 cm-1 (Aroney et al., 1955 see also Whetsel et al., 1956). Its frequency lies between the Raman frequency of dinitrogen (2330 cm-1, Schrotter, 1970) and the stretching vibration frequency of the C = N group in benzonitrile (2255 cm-1, Aroney et al., 1955). In substituted benzenediazonium salts the frequency of the NN stretching vibration follows Hammett op relationships. Electron donor substituents reduce the frequency, whereas acceptor substituents increase it. The 4-dimethylamino group, for example, shifts it by 103 cm-1 to 2177 cm-1 (Nuttall et al., 1961). This result supports the hypothesis that... 

Ethynylhydroxy carbene [13] has been obtained by photoreaction (A>400 nm) of a triatomic carbon cluster with water in an argon matrix and studied by IR spectroscopy (Ortman et al., 1990). Five frequencies were measured for [13] and a vibrational band at 1999.8 cm has been assigned to the C=C stretch. This value is more than 100 cmlower than the C=C stretching vibrations in acetylene derivatives, indicating that the C=C bond in the carbene [13] has lost some of its triple bond character. At the same... 

The well-known tetrahedral [Co(NCS)4]2 ion has continued to attract attention from analytical chemists, physical chemists, and spectroscopists. The inelastic electron tunneling (IET) spectrum of (Me4N)2[Co(NCS)4] was compared with IR and Raman spectra of the same complex.359 The vibrational bands due to the Me4N+ were prominent in all three spectra, but Coligand stretches were absent from the IET spectra. The lowest 4 42 4T2 electronic transition was strong in the IET spectrum but absent from the IR spectrum. The electric dipole allowed 4A2 4TX electronic transition was observed in both the IET and IR spectra and no fine structure was observed. Complex formation equilibria between Co11 and SCN- were studied calorimetri-... 

To help settle this controversey, Stavola et al. (1987) measured the H-stretching frequencies of acceptor-H complexes for B, Al, and Ga acceptors. Spectra are shown in Fig. 4. Distinct vibrational bands were... 

While the BC configuration for the B—H complex is now accepted, several aspects of the vibrational spectra of the acceptor-H complexes are not understood. The temperature dependence of the B—H complex has been examined by Raman spectroscopy (Stutzmann and Herrero, 1987) and IR absorption (Stavola et al., 1988a). The H-stretching vibration shifts from 1875 to 1903 cm 1 between room temperature and liquid He temperature. Frequency shifts of just a few cm 1 are more typical for local vibrational modes. The vibrational bands are also surprisingly broad. 

The assignment of the 809 and 1560 cm-1 bands of the donor-H complexes were based upon the expected frequencies of the wagging and stretching modes and the 2 1 ratio of intensities (Bergman et al., 1988a). A uniaxial stress study of the vibrational bands (Bergman et al., 1988b) will be reviewed here. Only the As—H complex was studied under stress because the donor-H complexes have nearly identical vibrational spectra for the different donors and are expected to behave similarly under stress. 

The stretching vibration band of the aldo-nitrone proton v=c-h is observed at 3140 cm-1, being 200 to 250 cm-1 higher than in the structurally similar imines. The stretching frequency decrease in v=c h, due to the unbonded interaction of the unshared nitrogen pair with the C-H bond has been determined (391). The presence in the IR-spectra of a strong band vch near 3100 cm-1 is a characteristic feature of cyclic aldo-nitrones (392). 

Absorption brought about by C-H bending is much more intense than that brought about by C=C stretching. The vibration band of C=C for cis forms is more intense than that for transforms. 

Here, the stretching and bending vibrational bands associated with specific structural or functional groups are observed frequently. 

In addition, our FTIR and XPS analyses of the nanoparticle samples showed that the removal of the capping shells from the surface of the bimetallic nanocrystalline core was very effective by the calcination treatment. The vibrational bands characteristic of the capping molecules in the C-H stretching region (VaCCHs) 2955 cm VjlCHs) 2872 cm Va(CH2) 2917 cm Vj(CH2) 2848 cm ) were not detected by FTIR for samples after calcination. XPS analysis of the calcined samples also showed no bands that can be associated with the presence of sulfur species (S(2pl/2) 163.8 eV, and S(2p3/2) 162.5 eV) on the nanoparticles surface. 

The FTIR reflection spectra of ethyl xanthate, and iron ethyl xanthate were reported to show the following characteristic absorption bands of ethyl xanthate the stretching vibration bands of the C—O—C at 1100- 1172 cm and C==S at 1049 cm and 1008 cm". When dixanthogen was formed, the stretching vibration bands changed. The characteristic absorption bands are 1260 cm" , 1240 cm", 1020 cm" and 1105 cm". When iron ethyl xanthate was formed, the stretching vibration band of C=S shifted to 1029 cm" and 1005 cm" (Mielezarski, 1997 Leppinen, 1990). 

It was reported that when lead ethyl xanthate was formed, the stretching vibration band of C=S shifted to 1018 and 996 cm . The stretching vibration band of C—O—C shifted to 1112 and 1207 cm" (Leppinen, 1990). 

As was mentioned in the preceding section, the infra-red stretching vibration bands of chalcogenoanions appear usually as more or less smeared-out bands. In contrcist, the infra-red spectra of small amounts of polyatomic anions isolated in eilkah halide host lattices have very sharp bands [see results in Refs. 204—209)]. Thus, one can clearly see that the bands are better defined when the anion can be effectively isolated and thereby ehminate the coupling between neighboring identical ions as well as reducing the other effects discussed earlier. More will be said about this in the next section. 

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