Low-lying excited states of HOOOCl and HOOOBr

A theoretical investigation of the low-lying singlet and triplet electronic states of HOOOCl and HOOOBr is presented. Calculations of excitation energies and oscillator strengths using CASSCF, first-order CI, MRCI and the equation of motion coupled-cluster singles and doubles methods are presented. The calculations predict that for HOOOCl and HOOOBr there are two singlet states that are accessible by wavelengths longer than 235 nm. These transitions, however, are predicted to be relatively weak. Spin–orbit calculations yield oscillator strengths for the lowest two triplet states of HOOOBr that are only one order of magnitude smaller than those of its low-lying singlet states. © 2000 American Institute of Physics. @S0021-9606~00!30518-9#