Triatomic molecule

Carbon dioxide

Triatomic molecules are molecules composed of three atoms, of either the same or different chemical elements. Examples include H₂O, CO₂ (pictured) and HCN.

Molecular vibrations

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

Symmetric linear molecules

A symmetric linear molecule ABA can perform:

Antisymmetric longitudinal vibrations with frequency

\omega _{a}={\sqrt {{\frac {k_{1}M}{m_{A}m_{B}}}}}

Symmetric longitudinal vibrations with frequency

\omega _{{s1}}={\sqrt {{\frac {k_{1}}{m_{A}}}}}

Symmetric transversal vibrations with frequency

\omega _{{s2}}={\sqrt {{\frac {2k_{2}M}{m_{A}m_{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.

Types

Homonuclear

Homonuclear triatomic molecules contain three of the same kind of atom.

Trihydrogen cation

Ozone

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 a Efimov state.^[1] Trisulfur (S₃) is analogous to ozone.

References

↑ Kunitski, M.; Zeller, S.; Voigtsberger, J.; Kalinin, A.; Schmidt, L. P. H.; Schoffler, M.; Czasch, A.; Schollkopf, W.; Grisenti, R. E.; Jahnke, T.; Blume, D.; Dorner, R. (30 April 2015). "Observation of the Efimov state of the helium trimer". Science. 348 (6234): 551–555. PMID 25931554. doi:10.1126/science.aaa5601.

Molecules detected in outer space

Molecules

Diatomic	Aluminium monochloride Aluminium monofluoride Aluminium monoxide Argonium Carbon monophosphide Carbon monosulfide Carbon monoxide Carborundum Cyanogen radical Diatomic carbon Fluoromethylidynium Hydrogen chloride Hydrogen fluoride Hydrogen (molecular) Hydroxyl radical Iron(II) oxide Magnesium monohydride cation Methylidyne radical Nitric oxide Nitrogen (molecular) Nitrogen monohydride Nitrogen sulfide Oxygen (molecular) Phosphorus monoxide Phosphorus mononitride Potassium chloride Silicon carbide Silicon mononitride Silicon monoxide Silicon monosulfide Sodium chloride Sodium iodide Sulfur monohydride Sulfur monoxide Titanium oxide
Triatomic	Aluminium hydroxide Aluminium isocyanide Amino radical Carbon dioxide Carbonyl sulfide CCP radical Chloronium Diazenylium Dicarbon monoxide Disilicon carbide Ethynyl radical Formyl radical Hydrogen cyanide (HCN) Hydrogen isocyanide (HNC) Hydrogen sulfide Hydroperoxyl Iron cyanide Isoformyl Magnesium cyanide Magnesium isocyanide Methylene radical N₂H⁺ Nitrous oxide Nitroxyl Ozone Phosphaethyne Potassium cyanide Protonated molecular hydrogen Sodium cyanide Sodium hydroxide Silicon carbonitride c-Silicon dicarbide Silicon naphthalocyanine Sulfur dioxide Thioformyl Thioxoethenylidene Titanium dioxide Tricarbon Water
Four atoms	Acetylene Ammonia Cyanic acid Cyanoethynyl Cyclopropynylidyne Formaldehyde Fulminic acid HCCN Hydrogen peroxide Hydromagnesium isocyanide Isocyanic acid Isothiocyanic acid Ketenyl Methylene amidogen Methyl radical Propynylidyne Protonated carbon dioxide Protonated hydrogen cyanide Silicon tricarbide Thioformaldehyde Tricarbon monoxide Tricarbon sulfide Thiocyanic acid
Five atoms	Ammonium ion Butadiynyl Carbodiimide Cyanamide Cyanoacetylene Cyanoformaldehyde Cyanomethyl Cyclopropenylidene Formic acid Isocyanoacetylene Ketene Methane Methoxy radical Methylenimine Propadienylidene Protonated formaldehyde Protonated formaldehyde Silane Silicon-carbide cluster
Six atoms	Acetonitrile Cyanobutadiynyl radical E-Cyanomethanimine Cyclopropenone Diacetylene Ethylene Formamide HC₄N Ketenimine Methanethiol Methanol Methyl isocyanide Pentynylidyne Propynal Protonated cyanoacetylene
Seven atoms	Acetaldehyde Acrylonitrile Vinyl cyanide Cyanodiacetylene Ethylene oxide Hexatriynyl radical Methylacetylene Methylamine Methyl isocyanate Vinyl alcohol
Eight atoms	Acetic acid Aminoacetonitrile Cyanoallene Ethanimine Glycolaldehyde Heptatrienyl radical Hexapentaenylidene Methylcyanoacetylene Methyl formate Propenal
Nine atoms	Acetamide Cyanohexatriyne Cyanotriacetylene Dimethyl ether Ethanol Methyldiacetylene Octatetraynyl radical Propene Propionitrile
Ten atoms or more	Acetone Benzene Buckminsterfullerene (C₆₀ fullerene, buckyball) C₇₀ fullerene Cyanodecapentayne Cyanopentaacetylene Cyanotetra-acetylene Ethylene glycol Ethyl formate Methyl acetate Methyl-cyano-diacetylene Methyltriacetylene Propanal n-Propyl cyanide Pyrimidine

Deuterated
molecules

Unconfirmed

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