Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Triatomic molecule

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Carbon dioxide

Triatomic molecules are formed by three atoms. Examples include H2O, CO2, HCN etc.

Molecular vibrations[edit]

The vibrational modes of a triatomic molecule can be determined in specific cases.

Symmetric linear molecules[edit]

A symmetric linear molecule ABA can perform:

  • Antisymmetric longitudinal vibrations with frequency
  • Symmetric longitudinal vibrations with frequency
  • Symmetric transversal vibrations with frequency

In the previous formulas, M is the total mass of the molecule, mA and mB are the masses of the elements A and B, k1 and k2 are the spring constants of the molecule along its axis and perpendicular to it.


Trihydrogen cation

Ozone, O3 is an example of a triatomic molecule with all atoms the same. Triatomic hydrogen, H3, is unstable and breaks up spontaneously. H3+, the trihydrogen cation is stable by itself and is symmetric.