Department of Chemistry

The Silicon Graphics Teaching Laboratory
has been replaced by the
Chemi cal Information Laboratory
and this information is for historical interest only

Normal Modes

A minimum energy conformation of a molecule will not be still, even at absolute zero of temperature, but will wobble around. These movements can be separated into a series of simple motions, called the normal modes, each of which corresponds to a particular frequency. Analysis of the normal modes allows us to see which motions have low energy, and which are less accessible.

Some examples are in the directory /usr/local/examples/NMA of the Silicon Graphics Teaching Laboratory. To see them, use the program Eadfrith. Make sure that NMA (option G) is switched on. When the molecule appears, you can see its normal vibrational modes by moving the mouse around with no buttons pressed. Pressing the mouse buttons manipulates the molecules in the normal way.

Normal mode analyses are given for water, methane, and a formaldehyde H2BCl complex. They were all calculated using ab initio molecular orbital theory.

The lowest normal mode of the complex of H2BF with formaldehyde