Normal Mode (Vibrational Mode)

Atoms are connected with each other so as to form a molecule, where electrons play a role as a spring to connect them. For diatomic molecules, there only exists stretching between two atoms. However, for tri-atomic (or more atoms) molecules, there exist stretching and bending activities among atoms. In general, for a molecule with N number of atoms, it has (3N-6) types of vibration modes. For a linear molecule, it has (3N-5) types of vibration modes. Depending on the change in a vibration mode, light with a particular wave is either emitted or absorbed. At this moment, emitted electromagnetic waves are infrared light.