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

asymmetric stretch

scissors

rocking

wagging

twisting

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.

Return to Chemistry, UWI-Mona, Home Page

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

Created October 1995. Last modified 4th February 2004.
URL http://wwwchem.uwimona.edu.jm/spectra/irvibs.html