Abstract We have calculated one-dimensional potential cuts of twenty-five singlet/triplet A ′/A″ states of ozone. The calculations are performed at the multi-reference configuration interaction level of electronic structure theory with the aug-cc-pVTZ set of atomic basis functions. It is found that many triplet potentials cross the 3 1 A ′( 1 B 2) potential, on which the fragmentation after excitation in the Huggins–Hartley band system primarily proceeds. These crossings allow the population of the three spin-forbidden product channels O( 3 P)+ O 2( a 1 Δ g ) , O( 3 P)+ O 2( b 1 Σ g +) and O( 1 D)+ O 2( X 3 Σ g −) . Possible consequences of singlet–triplet crossings for the Wulf band are also briefly discussed.