Sulfuroxide

Sulfuroxide, commonly called sulfur monoxide (SO), is a diatomic sulfur–oxygen radical. It is the simplest sulfur–oxygen compound that contains an unpaired electron, and as such is highly reactive and short‑lived under ordinary conditions.

Structure and bonding: SO is a linear diatomic molecule with a doublet Pi electronic ground state. The bond has significant multiple-bond character, and the molecule behaves as a reactive intermediate rather than a stable species.

Production and occurrence: In the gas phase, SO is produced by photolysis of sulfur dioxide (SO2) and by reactions of sulfur atoms with oxygen or oxygen-containing species. It is observed in combustion flames and volcanic plumes, and it has been detected in interstellar and circumstellar environments where sulfur chemistry occurs.

Reactions and chemistry: As a radical, SO readily reacts with O2, OH, NOx, and other radicals. It can add to O2 to form SO2, and it participates in catalytic cycles that control sulfur oxidation states in flames and atmospheres. Its transient nature means it is typically studied in situ or inferred from rapid spectroscopy and kinetics measurements.

Spectroscopy and detection: SO has been studied by infrared, microwave, and ultraviolet–visible spectroscopy. Because it is short‑lived, detection often relies on rapid spectroscopic techniques and on laboratory–theoretical studies of its potential energy surface and reaction kinetics.

Significance: SO is a key reactive intermediate in atmospheric and combustion chemistry and serves as a proxy for sulfur-containing radical chemistry in astrophysical environments.

Name: Sulfuroxide is an alternative historical name; sulfur monoxide is the preferred common name.