Dibromine monoxide is the chemical compound composed of bromine and oxygen with the formula Br<sub>2</sub>O. It is a dark brown solid which is stable below −40 ðC and is used in bromination reactions. It is similar to dichlorine monoxide, the monoxide of its halogen neighbor one period higher on the periodic table. The molecule is bent, with C<sub>2v</sub> molecular symmetry. The Br−O bond length is 1.85 àand the Br−O−Br bond angle is 112ð, similar to dichlorine monoxide.
Dibromine monoxide can be prepared by reacting bromine vapor or a solution of bromine in carbon tetrachloride with mercury(II) oxide at low temperatures:
It can also be formed by thermal decomposition of bromine dioxide or by passing an electrical current through a 1:5 mixture of bromine and oxygen gases.