Why does iodine form a violet vapour when it sublimes?

Iodine is a nonmetallic, nearly black solid at room temperature that consists of discrete diatomic molecules. Because it possesses a moderate vapor pressure, it undergoes sublimation—the process of transitioning directly from a solid to a gas—when exposed to air.1

The characteristic deep violet color of the resulting vapor is attributed to these uncoordinated iodine molecules, which retain their diatomic structure in the gaseous state. Similar violet-colored vapors and solutions are observed in inert solvents, such as carbon tetrachloride or carbon disulfide, where the iodine molecules also remain uncoordinated.1