I have done synthesis of ferric oxide by precipitation method and I have done a FTIR analysis. a peak appeared in ~525 cm-1 while another peak appeared in ~434cm-1 only. what is the meaning of them?
and, why is the peaks are only in foot print region?
The 525 cm-1 band is due to the Fe-O stretching and 434 cm-1 band is caused by the O-Fe-O bending mode. Since both Fe and O are rather heavy atoms, in particular Fe, the vibrational frequencies of harmonic oscillators that are connected by a single bond is rather small. When you have a light element, the frequency increases dramatically, such as CH stretching mode around 2900 cm-1. The number of the expected absorption modes for any molecules is 3N-6, provided that the molecular symmetry does not prohibit appearance in the spectrum. Thus, the molecule with no symmetry will follow this rule. Those groups that are missing in FTIR spectrum by the molecular symmetry can be observed by Raman spectroscopy.
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