Caesium ozonide

Caesium ozonide is an oxygen-rich chemical compound of caesium, with the chemical formula CsO3. It consists of caesium cations Cs+ and ozonide anions O3−. It can be formed by reacting ozone with caesium superoxide:


 * CsO2 + O3 → CsO3 + O2

The compound reacts strongly with any water in the air forming caesium hydroxide.


 * 4 CsO3 + 2 H2O → 4 CsOH + 5 O2

If heated to between 70 and 100 °C, caesium ozonide will quickly decompose to caesium superoxide (CsO2). In fact, the compound is metastable to decomposition into caesium superoxide, slowly decomposing at room temperature, but can remain intact for months if stored at −20 °C.

Above around 8 °C, the crystal structure is of the caesium chloride type, with the ozonide ion in place of the chloride ion. At lower temperatures, the crystal structure changes to a structure identical to rubidium ozonide (RbO3), with space group P21/c.