Vibrational splittings

In the complexes of lanthanide perrhenates with TMU (78), DMA (56), and DMF (46), it has been observed that the i>3(Re04) vibration splits into three bands in the region 900 cm-1. This indicates the presence of coordinated perrhenate group (either C3v or C2v symmetry). The ionic perrhenate group exhibits only one band in this region. 

Steadily in the order 359, 385, 395, and 402 nm. The emission spectra exhibit a clearer vibrational fine structure than the absorption spectra. For spiro-sexiphe-nyl, 35b, a detailed analysis shows that the vibrational splitting of 0.20 eV corresponds to a phenyl breathing mode in the Raman spectrum [108]. If for spiro-sexiphenyl the outer biphenyl moieties are fixed parallel as in 4-Spiro (43), the absorption maximum is shifted from 346 to 353 nm (amorphous films) and the fluorescence maximum from 420 to 429 nm, maintaining the Stokes shift. The corresponding spectra are shown in Figure 3.17. The absorption signal at 310 nm in the spectrum of 43 can be attributed to the terminal fluorene moieties. The quantum yields for the fluorescence in the amorphous film are 38% for 35b and as high as 70 10% for 43 [89]. 

Figure 17 shows the infrared spectra (from 1900 to 1200 cm-1) of the completely ionized calcium ionomer of an ethylene-methacrylic acid copolymer recorded at room temperature (a) and the same film recordered at 40, 70, 130, and 150 °C (b-e, respectively). This recording of the spectra at the elevated temperatures accentuates the sharp doublet at 1515/1548 cm which is characteristic of an interaction or vibrational splitting of the pairs of COO" groups. 

The peaks at 663 cm-1 and 1455 cm-1 belong to isomer 5(A), while the peaks at 637 cm-1 and 1509 cm-1 belong to isomer 5(B). The N-N stretch vibration splits only by a very small amount so that two peaks cannot be resolved by the experimental spectrum and only a single band appears at 1365 cm-1. 

The addition of alkali and alkaline earth metal perchlorates to AN causes in the region of the C-N stretching band of AN the appearance of a band produced by acetonitrile molecules in the solvation shells of the cations (fig. 1 for NaClOt solutions) a band of the originally triply degenerate antisymmetric Cl-O stretching vibration splits at increased salt concentration due to ion-aggregate formation (fig. 2, for a solution of LiClO ). The bands (a) and (b) in fig. 2 tire assigned to the free anions, band (1) is due to the vibration of a contact ion pair and band (2) to that of a solvent separated ion pair. Alkaline earth metal perchlorate solutions reveal in addition to the free anion bands (a) and (b) three bands due to [M + C10 )2Y,[M - C10 ]+ and [M + AN)C10 ]+,M + = Mg +,Ca +,Ba +. 

With this Hamiltonian, Pickett21) derived the same 0—1 vibrational splitting as that found earlier by Harris et al.18) and the same effective rotational constants as those obtained by Scharpen using perturbation theory20). 

Table II. Polysilylene Phosphorescence Origins and Vibrational Splittings...

In the case of trimethylene sulfide, Harris et al.22 were able to locate direct perturbation-induced transitions between the resonating n = 0 and n - 1 states. The value of the energy separation obtained agreed to within a few megahertz of that obtained using Eq. (14). A number of small vibrational splittings have been determined in this manner.11, 22,29 31 32... 

Table 2.2f lists vibrational frequencies of XXY-type molecules. Tables 2.2g and 2.2h list those of linear and bentXYZ-type molecules, respectively. It should be noted that the description of vibrational modes such as v(XX), v(XY), and v(YZ) is only qualitative. Most of these frequencies were measured in inert gas matrices. Some of these vibrations split into two because of Fermi resonance, matrix effect, or crystal, field effects. 

Substitution of one of the Y atoms of a pyramidal XY 3 molecule by a Z atom lowers the symmetry from C31, to Then the degenerate vibrations split into two bands, and all... 

Table ll-2e lists the vibrational frequencies of linear XYZ-typc molecules. Some of these vibrations split into two because of Fermi resonance or the crystal-held effect. Vibrational spectra of coordination compounds containing pseudohalide ions such as NCS, NCO", and NJ are discussed in Sec. Ill-15. 

Substiiution of one of the Y atoms of a pyramidal XYj molecule by a Z atom lowers the symmetry from Cj to C. Then the degenerate vibrations split into two bands, and all six vibrations become infrared and Raman active. The relationship between C3 and C is shown in Table II-3d. Table ll-3e lists the vibrational frequencies of pyramidal ZXY2 molecules. Simon and Paet-zold made an extensive study of the vibrational spectra of selenium compounds. The ZXYW-type molecule belongs to the C, point group, and all six vibrations are infrared and Raman active. The vibrational spectra of OSClBr and [XSnYZ] (X, Y, Z a halogen) have been reported. 

The free sulfate ion belongs to the liigh-symmetry point group Tj. Of the four fundamentals, only v- and P4 are infrared active. If the symmetry of the ion is lowered by complex formation, the degenerate vibrations split and... 

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