Carbon monoxide is a diatomic compound with the chemical composition CO. At terrestrial atmospheric pressure, the melting point of pure carbon monoxide is −205 °C and the boiling point is −191.5 °C.
Carbon monoxide is not known to occur as a pure substance in most planetary environments, but instead occurs primarily as a minor component in gas and ice mixtures. Carbon monoxide is the most abundant constituent after molecular hydrogen in interstellar space (see Molecules in Space), and spectroscopic observations indicate it composes several percent of the icy component of comets (which is predominantly water ice). These observations indicate carbon monoxide was a significant reservoir of carbon during formation of the solar system. In planetary bodies, carbon monoxide primarily occurs as a trace component in atmospheres (∼0.1 parts per million on the present Earth) and in volcanic gases.
Transformations between carbon monoxide and carbon dioxide (CO2)...