In order to simplify treatment of the ozone forming reaction a reduced dimensionality model is proposed, where the angle between two oxygen-oxygen bonds is relaxed for each pair of values of the bond lengths. This approach produces a two-dimensional potential energy surface which retains all major features of the ozone molecule, reproduces qualitatively the spectrum of van der Waals states important for the ozone formation process, and reproduces exactly the value of zero-point energy change (Delta ZPE) important for the anomalous isotope effect. Semiclassical treatment is employed to calculate properties of van der Waals states in the two isotopically different channels. (C) 2009 Elsevier B.V. All rights reserved.