Xenon trioxide is an unstable compound of xenon in its +6 oxidation state. It is a very powerful oxidizing agent, and liberates oxygen (and xenon) from water slowly, accelerated by exposure to sunlight. It is dangerously explosive upon contact with organic materials. When it dissolves in water, an acidic solution of xenic acid is formed:

XeO₃(aq) + H₂O → H₂XeO₄ ⇌ H⁺ + HXeO₄⁻

References

1. Webelements periodic table: page on Xenon(VI) oxide