Triatomic molecule

 ( Molecular Vibration ) 

Triatomic molecules are composed of three , of either the same or different . Examples include water, carbon dioxide (pictured), hydrogen cyanide, O₃ (ozone) and nitrogen dioxide.

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

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Symmetric linear molecules A symmetric linear molecule ABA can perform:

• Antisymmetric longitudinal vibrations with frequency

$\backslash omega\_a=\backslash sqrt\{\backslash frac\{k\_1M\}\{m\_Am\_B\}\}$

• Symmetric longitudinal vibrations with frequency

$\backslash omega\_\{s1\}=\backslash sqrt\{\backslash frac\{k\_1\}\{m\_A\}\}$

• Symmetric transversal vibrations with frequency

$\backslash omega\_\{s2\}=\backslash sqrt\{\backslash frac\{2k\_2M\}\{m\_Am\_B\}\}$

In the previous formulas, M is the total mass of the molecule, m_A and m_B 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.

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Types

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Homonuclear Homonuclear triatomic molecules contain three of the same kind of atom. That molecule will be an allotrope of that chemical element.

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. ⁴He₃, the helium trimer is only weakly bound by van der Waals force and is in an Efimov state. Trisulfur (S₃) is analogous to ozone.

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Geometry All triatomic molecules may be classified as possessing either a linear, bent, or cyclic geometry.

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Linear Linear triatomic molecules owe their geometry to their sp or sp³d hybridised central atoms. Well-known linear triatomic molecules include carbon dioxide (CO₂) and hydrogen cyanide (HCN).

Xenon difluoride (XeF₂) is one of the rare examples of a linear triatomic molecule possessing non-bonded pairs of electrons on the central atom.

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Bent

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Cyclic

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