We have performed new electronic structure calculations for the five lowest (1)A' states of ozone using the multi-reference configuration interaction method with an augmented triple zeta valence atomic basis set. Several avoided crossings, which are important for interpreting the Huggins-Hartley band system, are identified and two-dimensional diabatic potential energy surfaces are constructed. It is argued that the Huggins and the Hartley band systems are due to excitation of the same electronic state. (C) 2003 Elsevier B.V. All rights reserved.