Iodine sublimation. Elemental iodine exists as diatomic molecules (I2) which are a blue-black solid room temperature, but it readily sublimates to a violet gas. The iodine molecules are held together by the accumulated Van der Waals forces which act between adjacent molecules, which are the result of the uneven distribution of orbiting electrons around the iodine atoms of the iodine molecules. The iodine vapour has a characteristic violet colour and is denser than air resulting in the vapour rising and quickly falling towards the surface.