Methylidyne

Methylidyne refers to the methylidyne radical, the diatomic molecule CH. It is a highly reactive species comprising one carbon atom bonded to one hydrogen atom and possessing an unpaired electron. In chemical literature the term is often used interchangeably with the CH radical. Because of its radical nature, methylidyne is short-lived under ordinary conditions and is typically observed only in reactive environments such as high-temperature flames or the interstellar medium, where it can be detected spectroscopically.

The CH molecule has a ground electronic state designated X2Π and exhibits a bond order reflecting its strong C–H interaction, along with notable spin-orbit and rotational structure. It participates in numerous flame-chemistry reactions and serves as an important intermediate in hydrocarbon oxidation. CH is detectable via its electronic transitions in the visible region, most famously the CH A–X transition near 430 nanometers, which produces a characteristic emission band used in flame diagnostics. Rotational and vibrational transitions of CH are also observed in other spectral regions, including the infrared and microwave ranges.

In astrophysics, methylidyne is observed in the interstellar and circumstellar medium, where its spectral signatures help trace carbon chemistry and physical conditions in star-forming regions. Its abundance and reaction pathways inform models of chemical networks in space and in combustion research. The term historically emphasizes the radical’s role as a reactive intermediate rather than a stable compound.