In-plane mode

As the isoquinoline molecule reorients in the order listed above, the absorption of infrared radiation by the in-plane vibrational modes would be expected to increase, while that of the out-of-plane modes would be predicted to decrease (in accordance with the surface selection rule as described above). In the flat orientation there is no component of the dipole moment perpendicular to the surface for the in-plane modes, and under the surface selection rule these modes will not be able to absorb any of the incident radiation. However, as mentioned above, infrared active modes (and in some cases infrared forbidden transitions) can still be observed due to field-induced vibronic coupled infrared absorption (16-20). We have determined that this type of interaction is present in this particular system. 

The bending modes of the hydrogen bond should be above 1000 cm-1 for the in plane mode < (OH), and below this for the out of plane mode y(OH). The in plane mode was calculated to fall at 1457 cm-1 1235 and a band at 1460 cm-1 was allotted to this vibration. Other analysts discounted this assignment125 1325 in favour of its being v(C-O). Both <5(OH) and <5(OD) remain unidentified in the /8-diketones and it seems reasonable to infer that they are so because this vibration is coupled to some other mode. 

Semi-empirical calculations involving the QCFF/PI -f CISD method and ab initio calculations using the CASSCF and HF/6-31G methods have been used to calculate vibrational frequencies of the in-plane modes for thiophene derivatives <1994JCP(100)2571, 1991JCP(94)957, 1991JCP(94)965, 1991JCP(95)4783>. 

The most prominent features in NRVS spectra are the strong set of peaks in the middle portion of the spectrum, which are principally from the in-plane motion of iron. At this time, a complete general analysis ofthe in-plane modes is notpossible. However this is probably not a frnal state. A relationship between the frequencies of the in-plane modes, iron spin state, and coordination state can be reasonably expected and is qualitatively observed. The increasing database of NRVS measurements on oriented single crystals of iron porphyrins... 

Investigation of MbNO has illustrated the value of quantitative comparisons between NRVS and Raman isotope shift measurements. For a mode at 556 cm, the KED indicated 80-90% of mode energy localized on FeNO with primary involvement of the nitrosyl N atom (e = 0.8), while Fe motion dominated the KED of a second FeNO vibration at 451 cm. These results supported the attribution of Fe-NO stretching character to the 451 cm mode, with consequent sensitivity to the Fe-NO bond strength. For a Raman peak near 3 60 cm, NRV S signal in excess of that expected on the basis of the epg value estimated from isotope shift measurements was rationalized in terms of unresolved contributions from two in-plane modes. This conclusion would not be possible on the basis of either NRVS nor Raman measurements individually. 

Resonant raman spectroscopy has proved to be another valuable tool for the study of the structure of the polydiacetylene chain. Due to the resonance enhancement the spectra are compared to greatly simplified, infrared spectra and show as principle feature only the in-plane modes of the polymer chain. The correlation of the CsC and C = C stretching modes and their temperature dependence have been interpreted as resonances between the mesomeric structures (I) and (II) i32) Hoy(rever, a model using simple anharmonic force constants for the acetylene structure (II) is in good agreement with the experiment, e.g, the temperature and pressure dependence of the vibration frequency and the mechanical properties... 

The second-order Raman spectra from 1,700 to 3,300 cm are relatively weak and broad compared to the first order Raman spectra. There are many papers devoted to the second-order Raman processes in graphite [49, 59-62] and carbon nanotubes [8, 34, 63]. The interpretation of the spectral behavior of the second-order bands in terms of DR have been done [3, 64, 65]. The corresponding phonon is involved in an inter-valley scattering process of in-plane modes (LO or TO) around the K-points in the two-dimensional (2D) Brillouine zone (BZ, Fig. 7.4) [66, 67]. 

These spectra illustrate a number of features of INS spectra. In comparison with the infim-ed speetrum of benzene vapour, in solid benzene the out-of-plane C-H bending modes are shifted to higher wavenumbers (e.g. vn, 673 to 694 cm ). The shift is a consequence of intermolecular forces in the solid. The in-plane modes are not shifted. Out-of-plane C-H bending modes are shifted ftirther to higher wavenumbers for benzene in NaY (vn, 700 em" ). 

The infrared spectra of proteins exhibit absorption bands associated with their characteristic amide group, the structural unit common to ail molecules of this type (shown in Figure 6.2a). An isolated planar amide group gives rise to five in-plane modes and one out-of-plane normal mode. The in-plane modes are due to C=0 stretching, C— N... 

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