CASSCF and MRCI studies on the electronic excited states of CHBrO, CClBrO, and CBr2O

The potential energy curves for the low-lying excited states of CHBrO, CClBrO, and CBr2O have been computed using the complete active space self-consistent field (CASSCF) method. The vertical excitation energies for the excited states were calculated using the multireference internally contracted configuration interaction (MRCI) method with the cc-pVTZ and cc-pVTZ+spdf diffuse functions basis sets. The vertical excitation energies were also calculated with an ECP basis set. Results show that the first excited states for CHBrO, CClBrO, and CBr2O are slightly bound in the CX (X=H, Cl, and Br) coordinates. However, the first excited state exhibits predissociation (to ground state products) as a result of curve-crossing. Dissociation of CHBrO should result in Br atoms and HCO radicals, while in CClBrO, there are two competing channels for dissociation, namely, Cl+Br+CO and Br+ClCO. In CBr2O, photodissociation is predicted to result in the production of 2Br+CO.