Antisymmetric stretching vibration

The symmetric and antisymmetric stretching vibrations of methylamine can be viewed on Learning By Modeling... 

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. 

In a KI matrix the electronic absorption maximum of 82 - is observed at 400 nm, and the 88 stretching vibration by a Raman line at 594 cm k 83 shows a Raman line at 546 cm and an infrared absorption at 585 cm which were assigned to the symmetric and antisymmetric stretching vibrations, respectively. The bromides and iodides of Na, K, and Rb have also been used to trap 82 - but the wavenumbers of the 88 stretching vibration differ by as much as 18 cm- from the value in KI. The anion S3- has been trapped in the chlorides, bromides and iodides of Na, K, and Rb [120]. While the disulfide monoanion usually occupies a single anion vacancy [116, 122], the trisulfide radical anion prefers a trivacancy (one cation and two halide anions missing) [119]. 

Figure 12. Vibrational action spectra of V (OCO) in the OCO antisymmetric stretch region, (a) Spectrum obtained by monitoring depletion in the photofragment produced by irradiation at the vibronic origin at 15,801 cm The IR absorption near 2391.5 cm removes molecules from V[" = 0, leading to an 8% reduction in the fragment yield, (b) Spectrum obtained by monitoring enhancement in the VO+ photofragment signal as the IR laser is tuned, with the visible laser fixed at 15,777 cm (the Vj = 1 v" = 1 transition). The simulated spectrum gives a more precise value of the OCO antisymmetric stretch vibration in V" (OCO) of 2392.0 cm .

Monomeric iminoboranes exhibit a B-N bond order higher than unity due to p - p bonding between nitrogen and three-coordinate boron. This event results in an allene-type structure as shown in (I) exhibiting its antisymmetric stretching vibration around 1800 cm-1. This should have a predominant i>(CN) character, whereas in the symmetric mode of lower wavenumber the B-N charac-... 

Independent evidence for local stress is provided by measurements of the frequency of the antisymmetric stretching vibration of C02 eliminated in crystalline undecanoyl peroxide on photolysis (253). The results indicate that local pressures of tens of kilobars are established. This is very much larger than the lattice strain that has been considered as developing during the polymerization of diacetylenes (254). McBride points out (246) that virtually all reactions cause changes in shape that should create local stress in a solid, so that subsequent... 

The geometry and electronic structure of the azide ion, Nj, is quite similar to that of allene. The rotational strength observed for the antisymmetric stretching vibration of the azide (2025 cm ) in azidomethemoglobin A (Figure 25), measured by Marcott, et al., is —3 x 10 esu cm, with an anisotropy ratio 0.02 (115). These values are two orders of magnitude or more greater than normally observed for VCD. 

The IR spectrum of 133 was obtained by laser vaporization of graphite and subsequent condensation of the reaction products in solid argon at 10 K. However, only the most intense mode at 1695 cm could be detected. " The antisymmetric stretching vibration of the linear isomer 132 is observed at 1952 cm . " " The assignment could be corroborated by measuring the spectra of isotopically labeled compounds. In a more recent theoretical work, the UV spectra of 133 and 134 were calculated, " " but experimental data are lacking so far. 

In connection with the structure of carbonyl metal complexes, these bands seem to be the result of the symmetric and the antisymmetric stretching vibrations of two CO molecules bonded linearly with the same Pd(II) ion. Imelik et al. (23) have shown that palladium ions are trigonally coordinated in Si, sites (d Om-Pd = 2 A). Because of chemisorbed CO, the palladium ions acquire a trigonal bypyramidal coordination. 

Figure 1. The surface pressure-molecular area isotherm of the DPPC monolayer at 22 °C (Figure 1A, top) with the infrared frequencies of the CH, antisymmetric stretching vibration, plotted against molecular area for the DPPC monolayer (Figure IB, bottom).

In Figure 7 a comparison is made of the frequency of the CHj antisymmetric stretching vibration as a function of molecular area for DPPC monolayer films at the A/W and A/Ge interfaces. As described above, the frequency of (his vibration is related to the overall macromolecular conformation of the lipid hydrocarbon chains. For the condensed phase monolayer (-40-45 A2 molecule 1), the measured frequency of the transferred monolayer film is virtually the same as that of the in-situ monolayer at the same molecular area, indicating a highly ordered acyl chain, predominately all-trans in character. For LE films as well as films transferred in the LE-LC phase transition region, however, the measured frequency appears independent (within experimental uncertainty) of the surface pressure, or molecular area, at which the film was transferred. The hydrocarbon chains of these films are more disordered than those of the condensed phase transferred films. However, no such easy comparison can be made to the in-situ monolayers at comparable molecular areas. For the LE monolayers (> ca. 70 A2 molecule 1), the transferred monolayers are more ordered than the in-situ film. In the LE-LC phase transition region ( 55-70 A2 molecule 1), the opposite behavior occurs. 

Figure 7. The calculated frequency of the CH2 antisymmetric stretching vibration in the transferred DPPC monolayer films (solid circles) plotted against the molecular area at which the film was transferred. The frequency of this vibration for the in-situ monolayer film at the A/W interface is superimposed on the plot (open circles).

Carboxylate ionomers have been characterised with Fourier transform-infrared (FT-IR) in the region of antisymmetric stretching vibration of carboxylate anions. Figure 4.8 shows carboxylate ionomer [89] of ethylene methacrylic (4%) copolymer). 

Thus, the force constants of the bonds, the masses of the atoms, and the molecular geometry determine the frequencies and the relative motions of the atoms. Fig. 2.1-3 shows the three normal vibrations of the water molecule, the symmetric and the antisymmetric stretching vibration of the OH bonds, and Va, and the deformation vibration 6. The normal frequencies and normal coordinates, even of crystals and macromolecules, may be calculated as described in Sec. 5.2. In a symmetric molecule, the motion of symmetrically equivalent atoms is either symmetric or antisymmetric with respect to the symmetry operations (see Section 2.7). Since in the case of normal vibrations the center of gravity and the orientation of the molecular axes remain stationary, equivalent atoms move with the same amplitude. 

Figure 2.1-3 Motional degrees of freedom of the water molecule, T, are translations and Ri rotations of the whole molecule, i = x, y, z Os is the symmetric, Ua the antisymmetric stretching vibration, 6 the deformation vibration.

For the out-of-phase or antisymmetric stretching vibration, the ball with the mass m2 can be regarded as being split into two halves which are moving at the same frequency and phase (Fig. 2.5-1 b). Therefore, its frequency is given by ... 

Figure 4.1-3 Symmetric and antisymmetric stretching vibrations of zig-zag chains. In the C-C chain, both vibrations are IR inactive and Raman active (rule of mutual exclusion at the center of each bond there is a local center of symmetry). As the Si-O-Si chain vibrates, on the other hand, all Si atoms move against all O atoms both vibrations are IR active. Both vibrations are Raman allowed i/j causes the greater polarizability change. The frequencies of these vibrations are affected by the substituents the listed values correspond to polyethylene and polydimethylsiloxane, respectively (Fig. 4.1-2C).

---