Accurate multireference calculations of the electron affinity of NO, BO and O2

We report a systematic investigation of the adiabatic electron affinities (EA) of BO, NO and O2 using a specifically adapted massively parallel version of the configuration-selective configuration interaction method (MRCI) which permits the explicit treatment of the most important triple and quadruple excitations (TQ). We find the EA(BO)=2.52 eV, EA(NO)=0.015 eV and EA(O2)=0.39 eV in good agreement with experimental results. We elucidate the physical mechanism that is responsible for the failure of standard MRCI to quantitatively describe the EA of oxygen containing molecules.