Multireference complete active space self-consistent-field (CASSCF) and multireference CASSF second-order perturbation theory (MSCASPT2) calculations were performed on the ground state and a number of low-lying excited singlet and triplet states of chlorobenzene. The dual phosphorescence observed experimentally is clearly explained by the MSCASPT2 potential-energy curves. Experimental findings regarding the dissociation channels of chlorobenzene at 193, 248, and 266 nm are clarified from extensive theoretical information including all low-energy potential-energy curves. (C) 2004 American Institute of Physics.