The electronic states of BrOOCl were investigated using computational approaches. The three forms (trans-, cis-, and twist-forms) of BrOOCl were optimized at the couple-cluster CCSD(T) level of theory with cc-pVTZ basis set. The vertical excitation energies were calculated for the six singlet and two triplet excited states of BrOOCl at the complete active space self-consistent field level of theory and the multi-reference internally contracted configuration interaction level of theory. The scalar relativistic effect on the electronic states of BrO-OCl was estimated. The comparison was made for the electronic states of BrOOCl and BrOOBr. (c) 2006 Elsevier B.V. All rights reserved.