Infrared Spectroscopy and Modes of Vibrations

For a molecule to absorb infrared radiation it must undergo a net change in dipole moment as a result of vibrational or rotational motion.
Vibrations can be subdivided into two classes, depending on whether the bond length or angle is changing:

stretching (symmetric and asymmetric)
bending (scissoring, rocking, wagging and twisting)

The energies associated with rotational transitions are generally much smaller than that for vibrational transitions and the peaks are found below 300 cm^-1 . Typically, vibrational spectra are measured between 4000 cm^-1 to 650 cm^-1 for NaCl optics or 4000 cm^-1 to 450 cm^-1 for KBr optics.
These vibrational types can be demonstrated by selecting the buttons below:

symmetric stretch reset	asymmetric stretch reset	scissors reset
rocking reset	wagging reset	twisting reset

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Created and maintained by Dr. Robert J. Lancashire,
The Department of Chemistry, University of the West Indies,
Mona Campus, Kingston 7, Jamaica.

Created Dec 1998. Last modified 17th December-98.
URL http://wwwchem.uwimona.edu.jm:1104/spectra/iranim/irmodes.html