Cluster compounds vibrational frequency

Johnson et al. (132) have also discussed the validity or otherwise of such analogies. Spectra from the same type of surface species that give similar vibrational spectroscopic patterns can show readily measurable frequency variations that may be much more significant in reactivity terms. However, it seems clear that in many cases the overall spectral patterns of cluster-compound ligands do provide useful and reliable fingerprints for identifying the structures of surface species. 

Detailed vibrational studies have been carried out on several carbonyl cluster compounds. Both single crystal and Raman solution data have been obtained for M3(C0)i2 (M = Ru or Os), and small changes in frequency of the two-mode v(C0) A vibrations of these two carbonyls in mixed crystals have been used as indicators of the molecular geometry changes by which each species adapts to sites in the mixed crystal. Intermediates formed on the interaction of several Group VIII cluster carbonyls with oxide surfaces have also been characterised by spectroscopic means. 

Analysis of the vibrational structure and rotational contours of the LIF emission and excitation spectra offers the possibility of studying the conformational changes of the molecules and clusters upon excitation. However, the assignment of the low-frequency modes observed in the LIF excitation spectra of the investigated compounds is difficult in view of the complexity of the dialkylamino group which may... 

Synchrotron-based nuclear resonance methods have revealed the vibrational dynamics of the iron atom in numerous systems, including alloys, amorphous materials, nanomaterials, and materials under high pressure. The above-mentioned selectivity for the probe nucleus is particularly valuable for biological macromolecules, which may contain many thousands of atoms, but a localized active site is often the true center of interest. Since its availability, NRVS has been applied to study the vibrational dynamics of Fe in proteins, porphyrin model compounds, " and iron-sulfur clusters. It is shown that NRVS can provide frequencies, amplitudes, and directions for Fe vibrations in the samples. It helps to clarify mode assignments in vibrational spectra and reveals many important vibrational modes of Fe that cannot be seen by other methods. In particular, NRVS reveals low-frequency motions of the Fe down to below 100 cm that control biological reactions. The applications presented here use Fe as the probe nucleus, but the principle applies to other Mossbauer isotopes such as " Sn, Kr, Ni, and Zn if appropriate sources are available. 

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