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 by selecting the buttons below:
symmetric stretch
asymmetric stretch
Return to Index of IR files.
Some interpreted spectra that use CHIME for display of both IR and molecular structure have been generated. (WINDOWS only).

A useful tutorial on IR spectroscopy can be found at CSU Stanislaus.
IR pages on the Web are maintained at the College of Pharmacy at the University of Kentucky.

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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 22nd February, 2000.