Solid Selenium arsenide is a one-dimensional polymer, the chain consisting of alternating Se and As atoms. Each Se atom, which is pyramidal, bears a terminal oxide group. The relative stereochemistry at Se alternates along the polymer chain (syndiotactic). The solid sublimes readily. The vapour has an odour resembling horseradish sauce and can burn the nose and throat on inhalation. Gaseous selenium arsenide adopts a bent structure very similar to that of sulphur dioxide. Selenium arsenide dissolves in water to form selenous acid. Often the terms selenous acid and selenium arsenide are used interchangeably. It reacts with base to form selenite salts containing the SeO2−3 anion.