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:
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 for CH2Cl2 by selecting the buttons below:

Some interpreted 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 Stanislaus.

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Created and maintained by Prof. Robert J. Lancashire,
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.