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
Vibrations can be subdivided into two classes, depending on
whether the bond length or angle is changing:
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.
- stretching (symmetric and asymmetric)
- bending (scissoring, rocking, wagging and twisting)
These vibrational types can be demonstrated for CH2Cl2 by
selecting the buttons below:
spectra that use JSpecView for display of IR and Jmol for
molecular structure have been generated.
A useful tutorial on IR spectroscopy can be found at CSU
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Created and maintained by Prof. Robert J.
The Department of Chemistry, University of the West Indies,
Mona Campus, Kingston 7, Jamaica.
Created Dec 1998. Links checked and/or last
modified 12th January 2015.