Intro | Water | Ammonia | Methylene group |

Molecular Vibrations - Part III

Example 2 - Ammonia

Ammonia belongs to the point group C3v. As a molecule with 4 atoms there are 6 (3N-6) vibrational modes. The first three are stretching modes, the next two are bending modes and there is one deformation mode.

In many cases terminology like antisymetric stretch etc. is used. This has no connection to group theory. It has more to do with the visual perception of the vibrational mode.

Mode 1: Antisymmetric Stretch

Character type: E

NH3 Mode 1

Mode 2: Antisymmetric Stretch

Character type: E

Mode 1 and 2 are degenerate

NH3 Mode 2

Mode 3: Symmetric Stretch

Character type: A1

NH3 Mode 3

Mode 4: Bend

Character type: E

NH3 Mode 4

Top View

Mode 5: Bend

Character type: E

Mode 4 and 5 are degenerate

NH3 Mode 5

Top View

Mode 6: Deformation

Character Type: A1

NH3 Mode 6

 

©2005 Paul Kiprof, All Rights Reserved
Comments: pkiprof@d.umn.edu
Updated: December 2005