English
Adjective
triatomic
 (of a molecule etc) consisting of three atoms
 Ozone is a triatomic form of oxygen
See also

 I \, is the moment of
inertia of the molecule
For microscopic, atomiclevel systems like a
molecule, angular momentum can only have specific discrete values
given by

 L^2 = l(l+1) \hbar^2 \,
 where l is a positive integer and \hbar is Planck's
reduced constant.
Also, for a diatomic molecule the moment of
inertia is

 I = \mu r_^2 \,
 where

 \mu \, is the reduced mass
of the molecule and
 r_ \, is the average distance between the two atoms in the
molecule.
So, substituting the angular momentum and moment
of inertia into Erot, the rotational energy levels of a diatomic
molecule are given by:

 E_ = \frac \ \ \ \ \ l=0,1,2,... \,
Vibrational energies
Another way a diatomic molecule can move is to
have each atom oscillate  or
vibrate  along a
line (the bond) connecting the two atoms. The vibrational energy is
approximately that of a
quantum harmonic oscillator:

 E_ = \left(n+\frac \right)hf \ \ \ \ \ n=0,1,2,... \,
 where

 n is an integer
 h is Planck's
constant and
 f is the frequency
of the vibration.
Comparison between rotational and vibrational energy
spacings
The lowest rotational energy level of a diatomic
molecule occurs for l=0 and gives Erot = 0. For O2, the next
highest quantum level (l=1) has an energy of roughly:
This spacing between the lowest two rotational
energy levels of O2 is comparable to that of a
photon in the
microwave region of the
electromagnetic spectrum.
The lowest vibrational energy level occurs for
n=0, and a typical vibration frequency is 5 x 1013 Hz. Doing a
calculation similar to that above gives:

 E_ \approx 3 \times 10^ \ \mathrm \,.
So the spacing, and the energy of a typical
spectroscopic transition, between vibrational energy levels is
about 100 times greater than that of a typical transition between
rotational
energy levels.
Further reading
 Molecular Spectra and Molecular Structure
IV. Constants of Diatomic Molecules
 Physics For Scientists and Engineers : Vol.
1 (4th ed.)
See also
Notes and references
External links

Hyperphysics  Rotational Spectra of Rigid Rotor Molecules
 Hyperphysics
 Quantum Harmonic Oscillator
 3D Chem  Chemistry,
Structures, and 3D Molecules
 IUMSC  Indiana
University Molecular Structure Center
triatomic in Arabic: ثنائي الذرة
triatomic in Catalan: Molècula diatòmica
triatomic in Spanish: Diatómico
triatomic in Malayalam: ദ്വയാണുതന്മാത്ര
triatomic in Japanese: 二原子分子
triatomic in Russian: Двухатомная молекула
triatomic in Chinese: 双原子分子