Photochemistry of dibromine peroxide, BrOOBr

Abstract

The photochemistry of dibromine peroxide was investigated by means of mixed quantum–classical trajectory calculations on seven coupled potential energy surfaces. Photoexcited BrOOBr disintegrates rapidly, at a rate comparable with thermal decomposition. The rate constant is J = 9.7 × 10⁻² s⁻¹. The mechanism was investigated, and the final photolysis products are shown to be mainly 2Br + O₂, though there is a minor channel leading to 2BrO. Their formation involves an unusual intermolecular vibronic energy redistribution process. A hitherto unknown isomer of BrOOBr, the van der Waals complex O₂(a¹Δ_g)·Br₂(X¹Σ⁺_g), was found, which is more stable than the peroxide by 1.2 mE_h.